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   12.550%   $76.1738   $76.17   $76.15   $76.20  
  Purchase #2 $98.83   9.136%   $107.8591   $107.86   $107.85   $107.90  
  Purchase #3 $55.79   6.668%   $59.5101   $59.51   $59.50   $59.50  
  Purchase #4 $248.33   5.293%   $261.4741   $261.47   $261.45   $261.50  
  Purchase #5 $118.59   8.358%   $128.5018   $128.50   $128.50   $128.50  
  Purchase #6 $201.57   5.640%   $212.9385   $212.94   $212.95   $212.90  
  Purchase #7 $153.62   8.719%   $167.0141   $167.01   $167.00   $167.00  
  7 purchase totals = $944.41       $1,013.4715   $1,013.46   $1,013.40   $1,013.50