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 $60.28   11.145%   $66.9982   $67.00   $67.00   $67.00  
  Purchase #2 $222.68   7.173%   $238.6528   $238.65   $238.65   $238.70  
  Purchase #3 $142.34   10.292%   $156.9896   $156.99   $157.00   $157.00  
  Purchase #4 $140.40   8.575%   $152.4393   $152.44   $152.45   $152.40  
  Purchase #5 $211.76   7.854%   $228.3916   $228.39   $228.40   $228.40  
  Purchase #6 $74.92   8.690%   $81.4305   $81.43   $81.45   $81.40  
  Purchase #7 $28.27   13.374%   $32.0508   $32.05   $32.05   $32.10  
  7 purchase totals = $880.65       $956.9528   $956.95   $957.00   $957.00