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 $33.95   7.206%   $36.3964   $36.40   $36.40   $36.40  
  Purchase #2 $188.56   11.826%   $210.8591   $210.86   $210.85   $210.90  
  Purchase #3 $218.45   8.832%   $237.7435   $237.74   $237.75   $237.70  
  Purchase #4 $213.55   8.482%   $231.6633   $231.66   $231.65   $231.70  
  Purchase #5 $69.26   8.599%   $75.2157   $75.22   $75.20   $75.20  
  Purchase #6 $229.99   10.783%   $254.7898   $254.79   $254.80   $254.80  
  Purchase #7 $42.92   8.811%   $46.7017   $46.70   $46.70   $46.70  
  7 purchase totals = $996.68       $1,093.3695   $1,093.37   $1,093.35   $1,093.40