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 $48.46   12.852%   $54.6881   $54.69   $54.70   $54.70  
  Purchase #2 $169.84   3.412%   $175.6349   $175.63   $175.65   $175.60  
  Purchase #3 $92.48   7.154%   $99.096   $99.10   $99.10   $99.10  
  Purchase #4 $32.80   12.527%   $36.9089   $36.91   $36.90   $36.90  
  Purchase #5 $241.75   5.105%   $254.0913   $254.09   $254.10   $254.10  
  Purchase #6 $108.82   12.567%   $122.4954   $122.50   $122.50   $122.50  
  Purchase #7 $246.43   12.299%   $276.7384   $276.74   $276.75   $276.70  
  7 purchase totals = $940.58       $1,019.6530   $1,019.66   $1,019.70   $1,019.60