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 $171.35   6.698%   $182.827   $182.83   $182.85   $182.80  
  Purchase #2 $101.47   6.296%   $107.8586   $107.86   $107.85   $107.90  
  Purchase #3 $198.81   6.723%   $212.176   $212.18   $212.20   $212.20  
  Purchase #4 $182.26   11.588%   $203.3803   $203.38   $203.40   $203.40  
  Purchase #5 $17.63   6.126%   $18.71   $18.71   $18.70   $18.70  
  Purchase #6 $95.88   10.165%   $105.6262   $105.63   $105.65   $105.60  
  Purchase #7 $20.67   12.777%   $23.311   $23.31   $23.30   $23.30  
  7 purchase totals = $788.07       $853.8891   $853.90   $853.95   $853.90