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 $236.55   12.694%   $266.5777   $266.58   $266.60   $266.60  
  Purchase #2 $220.28   8.798%   $239.6602   $239.66   $239.65   $239.70  
  Purchase #3 $44.92   6.768%   $47.9602   $47.96   $47.95   $48.00  
  Purchase #4 $178.96   4.193%   $186.4638   $186.46   $186.45   $186.50  
  Purchase #5 $153.95   9.203%   $168.118   $168.12   $168.10   $168.10  
  Purchase #6 $129.91   6.792%   $138.7335   $138.73   $138.75   $138.70  
  Purchase #7 $95.45   12.772%   $107.6409   $107.64   $107.65   $107.60  
  7 purchase totals = $1,060.02       $1,155.1543   $1,155.15   $1,155.15   $1,155.20