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 $226.42   6.702%   $241.5947   $241.59   $241.60   $241.60  
  Purchase #2 $148.43   6.250%   $157.7069   $157.71   $157.70   $157.70  
  Purchase #3 $101.97   4.155%   $106.2069   $106.21   $106.20   $106.20  
  Purchase #4 $182.55   8.817%   $198.6454   $198.65   $198.65   $198.60  
  Purchase #5 $201.43   8.763%   $219.0813   $219.08   $219.10   $219.10  
  Purchase #6 $132.73   5.222%   $139.6612   $139.66   $139.65   $139.70  
  Purchase #7 $102.51   10.714%   $113.4929   $113.49   $113.50   $113.50  
  7 purchase totals = $1,096.04       $1,176.3893   $1,176.39   $1,176.40   $1,176.40