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 $15.33   4.576%   $16.0315   $16.03   $16.05   $16.00  
  Purchase #2 $214.29   10.346%   $236.4604   $236.46   $236.45   $236.50  
  Purchase #3 $61.44   9.234%   $67.1134   $67.11   $67.10   $67.10  
  Purchase #4 $72.85   7.481%   $78.2999   $78.30   $78.30   $78.30  
  Purchase #5 $218.53   7.788%   $235.5491   $235.55   $235.55   $235.50  
  Purchase #6 $88.69   4.612%   $92.7804   $92.78   $92.80   $92.80  
  Purchase #7 $240.60   6.796%   $256.9512   $256.95   $256.95   $257.00  
  7 purchase totals = $911.73       $983.1859   $983.18   $983.20   $983.20