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 $93.64   5.312%   $98.6142   $98.61   $98.60   $98.60  
  Purchase #2 $226.51   13.110%   $256.2055   $256.21   $256.20   $256.20  
  Purchase #3 $179.47   12.175%   $201.3205   $201.32   $201.30   $201.30  
  Purchase #4 $138.34   7.192%   $148.2894   $148.29   $148.30   $148.30  
  Purchase #5 $247.74   3.584%   $256.619   $256.62   $256.60   $256.60  
  Purchase #6 $187.48   11.640%   $209.3027   $209.30   $209.30   $209.30  
  Purchase #7 $168.72   12.593%   $189.9669   $189.97   $189.95   $190.00  
  7 purchase totals = $1,241.90       $1,360.3182   $1,360.32   $1,360.25   $1,360.30