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 $84.76   10.729%   $93.8539   $93.85   $93.85   $93.90  
  Purchase #2 $94.69   12.518%   $106.5433   $106.54   $106.55   $106.50  
  Purchase #3 $154.39   11.227%   $171.7234   $171.72   $171.70   $171.70  
  Purchase #4 $200.62   7.229%   $215.1228   $215.12   $215.10   $215.10  
  Purchase #5 $223.71   8.393%   $242.486   $242.49   $242.50   $242.50  
  Purchase #6 $231.31   4.553%   $241.8415   $241.84   $241.85   $241.80  
  Purchase #7 $174.60   6.476%   $185.9071   $185.91   $185.90   $185.90  
  7 purchase totals = $1,164.08       $1,257.4780   $1,257.47   $1,257.45   $1,257.40