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 $40.93   12.535%   $46.0606   $46.06   $46.05   $46.10  
  Purchase #2 $197.64   4.582%   $206.6959   $206.70   $206.70   $206.70  
  Purchase #3 $42.92   5.179%   $45.1428   $45.14   $45.15   $45.10  
  Purchase #4 $48.30   13.324%   $54.7355   $54.74   $54.75   $54.70  
  Purchase #5 $14.86   4.377%   $15.5104   $15.51   $15.50   $15.50  
  Purchase #6 $68.36   8.272%   $74.0147   $74.01   $74.00   $74.00  
  Purchase #7 $110.31   11.424%   $122.9118   $122.91   $122.90   $122.90  
  7 purchase totals = $523.32       $565.0717   $565.07   $565.05   $565.00