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 $152.93   9.505%   $167.466   $167.47   $167.45   $167.50  
  Purchase #2 $216.72   13.838%   $246.7097   $246.71   $246.70   $246.70  
  Purchase #3 $68.48   11.749%   $76.5257   $76.53   $76.55   $76.50  
  Purchase #4 $229.34   12.104%   $257.0993   $257.10   $257.10   $257.10  
  Purchase #5 $195.81   9.389%   $214.1946   $214.19   $214.20   $214.20  
  Purchase #6 $63.35   7.636%   $68.1874   $68.19   $68.20   $68.20  
  Purchase #7 $176.85   6.672%   $188.6494   $188.65   $188.65   $188.60  
  7 purchase totals = $1,103.48       $1,218.8321   $1,218.84   $1,218.85   $1,218.80