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 $148.74   6.592%   $158.5449   $158.54   $158.55   $158.50  
  Purchase #2 $210.93   7.417%   $226.5747   $226.57   $226.55   $226.60  
  Purchase #3 $58.98   12.840%   $66.553   $66.55   $66.55   $66.60  
  Purchase #4 $250.94   13.541%   $284.9198   $284.92   $284.90   $284.90  
  Purchase #5 $187.25   13.545%   $212.613   $212.61   $212.60   $212.60  
  Purchase #6 $86.60   10.763%   $95.9208   $95.92   $95.90   $95.90  
  Purchase #7 $109.48   6.362%   $116.4451   $116.45   $116.45   $116.40  
  7 purchase totals = $1,052.92       $1,161.5713   $1,161.56   $1,161.50   $1,161.50