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 $209.43   10.628%   $231.6882   $231.69   $231.70   $231.70  
  Purchase #2 $150.87   13.243%   $170.8497   $170.85   $170.85   $170.80  
  Purchase #3 $63.32   3.335%   $65.4317   $65.43   $65.45   $65.40  
  Purchase #4 $146.99   9.774%   $161.3568   $161.36   $161.35   $161.40  
  Purchase #5 $65.25   3.467%   $67.5122   $67.51   $67.50   $67.50  
  Purchase #6 $210.71   12.360%   $236.7538   $236.75   $236.75   $236.80  
  Purchase #7 $120.82   9.128%   $131.8484   $131.85   $131.85   $131.80  
  7 purchase totals = $967.39       $1,065.4408   $1,065.44   $1,065.45   $1,065.40