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 $89.91   5.587%   $94.9333   $94.93   $94.95   $94.90  
  Purchase #2 $45.37   9.109%   $49.5028   $49.50   $49.50   $49.50  
  Purchase #3 $220.60   12.257%   $247.6389   $247.64   $247.65   $247.60  
  Purchase #4 $98.30   4.397%   $102.6223   $102.62   $102.60   $102.60  
  Purchase #5 $206.32   5.314%   $217.2838   $217.28   $217.30   $217.30  
  Purchase #6 $116.59   13.508%   $132.339   $132.34   $132.35   $132.30  
  Purchase #7 $159.80   11.499%   $178.1754   $178.18   $178.20   $178.20  
  7 purchase totals = $936.89       $1,022.4955   $1,022.49   $1,022.55   $1,022.40