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 $205.27   11.701%   $229.2886   $229.29   $229.30   $229.30  
  Purchase #2 $139.73   3.737%   $144.9517   $144.95   $144.95   $145.00  
  Purchase #3 $86.43   7.320%   $92.7567   $92.76   $92.75   $92.80  
  Purchase #4 $117.91   12.399%   $132.5297   $132.53   $132.55   $132.50  
  Purchase #5 $145.63   10.137%   $160.3925   $160.39   $160.40   $160.40  
  Purchase #6 $237.80   3.662%   $246.5082   $246.51   $246.50   $246.50  
  Purchase #7 $35.80   6.771%   $38.224   $38.22   $38.20   $38.20  
  7 purchase totals = $968.57       $1,044.6514   $1,044.65   $1,044.65   $1,044.70