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 $149.66   12.229%   $167.9619   $167.96   $167.95   $168.00  
  Purchase #2 $186.50   9.192%   $203.6431   $203.64   $203.65   $203.60  
  Purchase #3 $96.25   6.702%   $102.7007   $102.70   $102.70   $102.70  
  Purchase #4 $25.62   7.817%   $27.6227   $27.62   $27.60   $27.60  
  Purchase #5 $192.44   12.494%   $216.4835   $216.48   $216.50   $216.50  
  Purchase #6 $111.30   3.722%   $115.4426   $115.44   $115.45   $115.40  
  Purchase #7 $47.78   6.809%   $51.0333   $51.03   $51.05   $51.00  
  7 purchase totals = $809.55       $884.8878   $884.87   $884.90   $884.80