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 $41.36   12.299%   $46.4469   $46.45   $46.45   $46.40  
  Purchase #2 $153.54   6.344%   $163.2806   $163.28   $163.30   $163.30  
  Purchase #3 $170.38   13.601%   $193.5534   $193.55   $193.55   $193.60  
  Purchase #4 $43.34   3.690%   $44.9392   $44.94   $44.95   $44.90  
  Purchase #5 $87.61   9.618%   $96.0363   $96.04   $96.05   $96.00  
  Purchase #6 $198.72   5.410%   $209.4708   $209.47   $209.45   $209.50  
  Purchase #7 $247.39   12.455%   $278.2024   $278.20   $278.20   $278.20  
  7 purchase totals = $942.34       $1,031.9296   $1,031.93   $1,031.95   $1,031.90