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 $250.35   10.380%   $276.3363   $276.34   $276.35   $276.30  
  Purchase #2 $41.91   7.240%   $44.9443   $44.94   $44.95   $44.90  
  Purchase #3 $54.45   11.227%   $60.5631   $60.56   $60.55   $60.60  
  Purchase #4 $131.70   5.108%   $138.4272   $138.43   $138.45   $138.40  
  Purchase #5 $21.52   6.110%   $22.8349   $22.83   $22.85   $22.80  
  Purchase #6 $151.48   4.553%   $158.3769   $158.38   $158.40   $158.40  
  Purchase #7 $231.31   11.668%   $258.2993   $258.30   $258.30   $258.30  
  7 purchase totals = $882.72       $959.7820   $959.78   $959.85   $959.70