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 $152.66   6.166%   $162.073   $162.07   $162.05   $162.10  
  Purchase #2 $81.27   13.282%   $92.0643   $92.06   $92.05   $92.10  
  Purchase #3 $244.56   12.341%   $274.7411   $274.74   $274.75   $274.70  
  Purchase #4 $91.66   10.674%   $101.4438   $101.44   $101.45   $101.40  
  Purchase #5 $48.52   8.110%   $52.455   $52.46   $52.45   $52.50  
  Purchase #6 $58.97   3.190%   $60.8511   $60.85   $60.85   $60.90  
  Purchase #7 $11.26   10.542%   $12.447   $12.45   $12.45   $12.40  
  7 purchase totals = $688.90       $756.0753   $756.07   $756.05   $756.10