Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $215.51   10.467%   $238.0674   $238.07   $238.05   $238.10  
  Purchase #2 $218.75   11.839%   $244.6478   $244.65   $244.65   $244.60  
  Purchase #3 $101.57   12.811%   $114.5821   $114.58   $114.60   $114.60  
  Purchase #4 $206.66   11.561%   $230.552   $230.55   $230.55   $230.60  
  Purchase #5 $244.39   10.247%   $269.4326   $269.43   $269.45   $269.40  
  Purchase #6 $80.49   11.412%   $89.6755   $89.68   $89.70   $89.70  
  Purchase #7 $242.46   10.606%   $268.1753   $268.18   $268.20   $268.20  
  7 purchase totals = $1,309.83       $1,455.1327   $1,455.14   $1,455.20   $1,455.20