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 $204.81   10.837%   $227.0053   $227.01   $227.00   $227.00  
  Purchase #2 $87.66   6.699%   $93.5323   $93.53   $93.55   $93.50  
  Purchase #3 $104.85   5.583%   $110.7038   $110.70   $110.70   $110.70  
  Purchase #4 $27.69   7.399%   $29.7388   $29.74   $29.75   $29.70  
  Purchase #5 $8.59   11.536%   $9.5809   $9.58   $9.60   $9.60  
  Purchase #6 $109.53   9.472%   $119.9047   $119.90   $119.90   $119.90  
  Purchase #7 $34.67   9.229%   $37.8697   $37.87   $37.85   $37.90  
  7 purchase totals = $577.80       $628.3355   $628.33   $628.35   $628.30