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 $119.97   4.830%   $125.7646   $125.76   $125.75   $125.80  
  Purchase #2 $5.73   8.366%   $6.2094   $6.21   $6.20   $6.20  
  Purchase #3 $100.55   11.180%   $111.7915   $111.79   $111.80   $111.80  
  Purchase #4 $149.33   9.547%   $163.5865   $163.59   $163.60   $163.60  
  Purchase #5 $50.28   13.841%   $57.2393   $57.24   $57.25   $57.20  
  Purchase #6 $131.88   6.581%   $140.559   $140.56   $140.55   $140.60  
  Purchase #7 $234.65   11.317%   $261.2053   $261.21   $261.20   $261.20  
  7 purchase totals = $792.39       $866.3556   $866.36   $866.35   $866.40