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 $62.50   6.824%   $66.765   $66.77   $66.75   $66.80  
  Purchase #2 $224.45   10.664%   $248.3853   $248.39   $248.40   $248.40  
  Purchase #3 $170.42   7.861%   $183.8167   $183.82   $183.80   $183.80  
  Purchase #4 $43.31   3.361%   $44.7656   $44.77   $44.75   $44.80  
  Purchase #5 $118.90   13.143%   $134.527   $134.53   $134.55   $134.50  
  Purchase #6 $119.91   7.292%   $128.6538   $128.65   $128.65   $128.70  
  Purchase #7 $45.58   6.141%   $48.3791   $48.38   $48.40   $48.40  
  7 purchase totals = $785.07       $855.2925   $855.31   $855.30   $855.40