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 $152.44   6.373%   $162.155   $162.16   $162.15   $162.20  
  Purchase #2 $27.28   11.613%   $30.448   $30.45   $30.45   $30.40  
  Purchase #3 $11.73   7.691%   $12.6322   $12.63   $12.65   $12.60  
  Purchase #4 $191.87   6.613%   $204.5584   $204.56   $204.55   $204.60  
  Purchase #5 $51.41   6.298%   $54.6478   $54.65   $54.65   $54.60  
  Purchase #6 $179.85   5.732%   $190.159   $190.16   $190.15   $190.20  
  Purchase #7 $154.61   6.259%   $164.287   $164.29   $164.30   $164.30  
  7 purchase totals = $769.19       $818.8874   $818.90   $818.90   $818.90