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 $242.79   13.197%   $274.831   $274.83   $274.85   $274.80  
  Purchase #2 $94.75   3.215%   $97.7962   $97.80   $97.80   $97.80  
  Purchase #3 $91.71   12.310%   $102.9995   $103.00   $103.00   $103.00  
  Purchase #4 $27.92   8.689%   $30.346   $30.35   $30.35   $30.30  
  Purchase #5 $193.70   11.367%   $215.7179   $215.72   $215.70   $215.70  
  Purchase #6 $105.75   4.591%   $110.605   $110.61   $110.60   $110.60  
  Purchase #7 $50.46   5.419%   $53.1944   $53.19   $53.20   $53.20  
  7 purchase totals = $807.08       $885.4900   $885.50   $885.50   $885.40