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 $38.93   13.266%   $44.0945   $44.09   $44.10   $44.10  
  Purchase #2 $169.85   8.213%   $183.7998   $183.80   $183.80   $183.80  
  Purchase #3 $193.32   13.433%   $219.2887   $219.29   $219.30   $219.30  
  Purchase #4 $143.38   8.470%   $155.5243   $155.52   $155.50   $155.50  
  Purchase #5 $250.40   7.334%   $268.7643   $268.76   $268.75   $268.80  
  Purchase #6 $247.43   11.262%   $275.2956   $275.30   $275.30   $275.30  
  Purchase #7 $54.39   11.660%   $60.7319   $60.73   $60.75   $60.70  
  7 purchase totals = $1,097.70       $1,207.4991   $1,207.49   $1,207.50   $1,207.50