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 $182.86   8.136%   $197.7375   $197.74   $197.75   $197.70  
  Purchase #2 $53.87   5.477%   $56.8205   $56.82   $56.80   $56.80  
  Purchase #3 $68.78   4.605%   $71.9473   $71.95   $71.95   $71.90  
  Purchase #4 $238.40   11.867%   $266.6909   $266.69   $266.70   $266.70  
  Purchase #5 $228.61   7.825%   $246.4987   $246.50   $246.50   $246.50  
  Purchase #6 $149.75   5.604%   $158.142   $158.14   $158.15   $158.10  
  Purchase #7 $96.53   9.638%   $105.8336   $105.83   $105.85   $105.80  
  7 purchase totals = $1,018.80       $1,103.6705   $1,103.67   $1,103.70   $1,103.50