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 $41.66   13.242%   $47.1766   $47.18   $47.20   $47.20  
  Purchase #2 $112.48   12.402%   $126.4298   $126.43   $126.45   $126.40  
  Purchase #3 $67.97   6.266%   $72.229   $72.23   $72.25   $72.20  
  Purchase #4 $45.86   7.820%   $49.4463   $49.45   $49.45   $49.40  
  Purchase #5 $237.30   8.450%   $257.3519   $257.35   $257.35   $257.40  
  Purchase #6 $145.89   4.468%   $152.4084   $152.41   $152.40   $152.40  
  Purchase #7 $208.29   4.638%   $217.9505   $217.95   $217.95   $218.00  
  7 purchase totals = $859.45       $922.9925   $923.00   $923.05   $923.00