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 $140.36   8.254%   $151.9453   $151.95   $151.95   $151.90  
  Purchase #2 $133.68   11.784%   $149.4329   $149.43   $149.45   $149.40  
  Purchase #3 $217.80   12.570%   $245.1775   $245.18   $245.20   $245.20  
  Purchase #4 $247.49   7.392%   $265.7845   $265.78   $265.80   $265.80  
  Purchase #5 $56.46   5.683%   $59.6686   $59.67   $59.65   $59.70  
  Purchase #6 $11.90   13.294%   $13.482   $13.48   $13.50   $13.50  
  Purchase #7 $88.74   7.513%   $95.407   $95.41   $95.40   $95.40  
  7 purchase totals = $896.43       $980.8978   $980.90   $980.95   $980.90