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 $248.97   13.522%   $282.6357   $282.64   $282.65   $282.60  
  Purchase #2 $211.56   5.271%   $222.7113   $222.71   $222.70   $222.70  
  Purchase #3 $71.89   13.774%   $81.7921   $81.79   $81.80   $81.80  
  Purchase #4 $174.85   6.520%   $186.2502   $186.25   $186.25   $186.30  
  Purchase #5 $102.35   6.864%   $109.3753   $109.38   $109.40   $109.40  
  Purchase #6 $145.28   6.474%   $154.6854   $154.69   $154.70   $154.70  
  Purchase #7 $13.80   7.738%   $14.8678   $14.87   $14.85   $14.90  
  7 purchase totals = $968.70       $1,052.3178   $1,052.33   $1,052.35   $1,052.40