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 $154.98   5.723%   $163.8495   $163.85   $163.85   $163.80  
  Purchase #2 $6.63   10.177%   $7.3047   $7.30   $7.30   $7.30  
  Purchase #3 $237.26   4.612%   $248.2024   $248.20   $248.20   $248.20  
  Purchase #4 $88.69   6.323%   $94.2979   $94.30   $94.30   $94.30  
  Purchase #5 $239.80   12.331%   $269.3697   $269.37   $269.35   $269.40  
  Purchase #6 $73.50   7.542%   $79.0434   $79.04   $79.05   $79.00  
  Purchase #7 $125.73   11.177%   $139.7828   $139.78   $139.80   $139.80  
  7 purchase totals = $926.59       $1,001.8504   $1,001.84   $1,001.85   $1,001.80