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 $211.60   11.637%   $236.2239   $236.22   $236.20   $236.20  
  Purchase #2 $76.91   13.867%   $87.5751   $87.58   $87.60   $87.60  
  Purchase #3 $169.95   4.339%   $177.3241   $177.32   $177.30   $177.30  
  Purchase #4 $199.76   5.654%   $211.0544   $211.05   $211.05   $211.10  
  Purchase #5 $170.65   8.723%   $185.5358   $185.54   $185.55   $185.50  
  Purchase #6 $66.39   11.344%   $73.9213   $73.92   $73.90   $73.90  
  Purchase #7 $224.92   10.258%   $247.9923   $247.99   $248.00   $248.00  
  7 purchase totals = $1,120.18       $1,219.6269   $1,219.62   $1,219.60   $1,219.60