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 $76.63   11.458%   $85.4103   $85.41   $85.40   $85.40  
  Purchase #2 $54.25   9.228%   $59.2562   $59.26   $59.25   $59.30  
  Purchase #3 $112.90   8.403%   $122.387   $122.39   $122.40   $122.40  
  Purchase #4 $248.30   13.151%   $280.9539   $280.95   $280.95   $281.00  
  Purchase #5 $207.85   10.433%   $229.535   $229.54   $229.55   $229.50  
  Purchase #6 $34.31   5.395%   $36.161   $36.16   $36.15   $36.20  
  Purchase #7 $184.62   9.569%   $202.2863   $202.29   $202.30   $202.30  
  7 purchase totals = $918.86       $1,015.9897   $1,016.00   $1,016.00   $1,016.10