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 $234.93   11.207%   $261.2586   $261.26   $261.25   $261.30  
  Purchase #2 $113.80   6.671%   $121.3916   $121.39   $121.40   $121.40  
  Purchase #3 $224.48   11.421%   $250.1179   $250.12   $250.10   $250.10  
  Purchase #4 $43.80   3.732%   $45.4346   $45.43   $45.45   $45.40  
  Purchase #5 $63.35   8.195%   $68.5415   $68.54   $68.55   $68.50  
  Purchase #6 $48.26   6.443%   $51.3694   $51.37   $51.35   $51.40  
  Purchase #7 $58.41   4.832%   $61.2324   $61.23   $61.25   $61.20  
  7 purchase totals = $787.03       $859.3460   $859.34   $859.35   $859.30