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 $228.98   7.804%   $246.8496   $246.85   $246.85   $246.80  
  Purchase #2 $65.39   9.644%   $71.6962   $71.70   $71.70   $71.70  
  Purchase #3 $80.68   4.172%   $84.046   $84.05   $84.05   $84.00  
  Purchase #4 $173.44   6.838%   $185.2998   $185.30   $185.30   $185.30  
  Purchase #5 $142.45   8.466%   $154.5098   $154.51   $154.50   $154.50  
  Purchase #6 $28.42   13.327%   $32.2075   $32.21   $32.20   $32.20  
  Purchase #7 $208.45   7.322%   $223.7127   $223.71   $223.70   $223.70  
  7 purchase totals = $927.81       $998.3216   $998.33   $998.30   $998.20