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 $196.94   10.565%   $217.7467   $217.75   $217.75   $217.70  
  Purchase #2 $8.64   13.393%   $9.7972   $9.80   $9.80   $9.80  
  Purchase #3 $21.69   10.286%   $23.921   $23.92   $23.90   $23.90  
  Purchase #4 $52.84   8.609%   $57.389   $57.39   $57.40   $57.40  
  Purchase #5 $51.98   13.726%   $59.1148   $59.11   $59.10   $59.10  
  Purchase #6 $189.42   7.709%   $204.0224   $204.02   $204.00   $204.00  
  Purchase #7 $73.59   11.401%   $81.98   $81.98   $82.00   $82.00  
  7 purchase totals = $595.10       $653.9711   $653.97   $653.95   $653.90