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 $118.46   11.708%   $132.3293   $132.33   $132.35   $132.30  
  Purchase #2 $51.55   7.504%   $55.4183   $55.42   $55.40   $55.40  
  Purchase #3 $68.75   12.524%   $77.3603   $77.36   $77.35   $77.40  
  Purchase #4 $206.79   9.335%   $226.0938   $226.09   $226.10   $226.10  
  Purchase #5 $154.82   5.192%   $162.8583   $162.86   $162.85   $162.90  
  Purchase #6 $241.87   9.159%   $264.0229   $264.02   $264.00   $264.00  
  Purchase #7 $221.27   11.683%   $247.121   $247.12   $247.10   $247.10  
  7 purchase totals = $1,063.51       $1,165.2039   $1,165.20   $1,165.15   $1,165.20