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 $67.68   3.389%   $69.9737   $69.97   $69.95   $70.00  
  Purchase #2 $201.87   8.143%   $218.3083   $218.31   $218.30   $218.30  
  Purchase #3 $118.93   3.608%   $123.221   $123.22   $123.20   $123.20  
  Purchase #4 $236.75   7.758%   $255.1171   $255.12   $255.10   $255.10  
  Purchase #5 $226.62   4.352%   $236.4825   $236.48   $236.50   $236.50  
  Purchase #6 $218.60   12.492%   $245.9075   $245.91   $245.90   $245.90  
  Purchase #7 $110.41   9.746%   $121.1706   $121.17   $121.15   $121.20  
  7 purchase totals = $1,180.86       $1,270.1807   $1,270.18   $1,270.10   $1,270.20