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 $203.83   10.766%   $225.7743   $225.77   $225.75   $225.80  
  Purchase #2 $44.59   11.342%   $49.6474   $49.65   $49.65   $49.60  
  Purchase #3 $30.28   12.709%   $34.1283   $34.13   $34.15   $34.10  
  Purchase #4 $30.40   7.146%   $32.5724   $32.57   $32.55   $32.60  
  Purchase #5 $66.81   9.449%   $73.1229   $73.12   $73.10   $73.10  
  Purchase #6 $67.69   11.465%   $75.4507   $75.45   $75.45   $75.50  
  Purchase #7 $197.71   6.489%   $210.5394   $210.54   $210.55   $210.50  
  7 purchase totals = $641.31       $701.2354   $701.23   $701.20   $701.20