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 $92.72   11.282%   $103.1807   $103.18   $103.20   $103.20  
  Purchase #2 $85.60   9.478%   $93.7132   $93.71   $93.70   $93.70  
  Purchase #3 $62.92   3.118%   $64.8818   $64.88   $64.90   $64.90  
  Purchase #4 $124.28   11.791%   $138.9339   $138.93   $138.95   $138.90  
  Purchase #5 $228.96   13.448%   $259.7505   $259.75   $259.75   $259.80  
  Purchase #6 $214.53   12.477%   $241.2969   $241.30   $241.30   $241.30  
  Purchase #7 $227.63   7.657%   $245.0596   $245.06   $245.05   $245.10  
  7 purchase totals = $1,036.64       $1,146.8166   $1,146.81   $1,146.85   $1,146.90