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 $68.87   13.681%   $78.2921   $78.29   $78.30   $78.30  
  Purchase #2 $33.57   10.521%   $37.1019   $37.10   $37.10   $37.10  
  Purchase #3 $59.93   7.772%   $64.5878   $64.59   $64.60   $64.60  
  Purchase #4 $86.52   13.197%   $97.938   $97.94   $97.95   $97.90  
  Purchase #5 $130.99   3.798%   $135.965   $135.97   $135.95   $136.00  
  Purchase #6 $211.45   7.171%   $226.6131   $226.61   $226.60   $226.60  
  Purchase #7 $212.73   12.341%   $238.983   $238.98   $239.00   $239.00  
  7 purchase totals = $804.06       $879.4809   $879.48   $879.50   $879.50