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 $52.67   3.301%   $54.4086   $54.41   $54.40   $54.40  
  Purchase #2 $185.36   7.815%   $199.8459   $199.85   $199.85   $199.80  
  Purchase #3 $124.76   8.689%   $135.6004   $135.60   $135.60   $135.60  
  Purchase #4 $230.29   12.787%   $259.7372   $259.74   $259.75   $259.70  
  Purchase #5 $211.65   8.784%   $230.2413   $230.24   $230.25   $230.20  
  Purchase #6 $181.56   11.825%   $203.0295   $203.03   $203.05   $203.00  
  Purchase #7 $114.58   7.412%   $123.0727   $123.07   $123.05   $123.10  
  7 purchase totals = $1,100.87       $1,205.9356   $1,205.94   $1,205.95   $1,205.80