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 $186.35   8.554%   $202.2904   $202.29   $202.30   $202.30  
  Purchase #2 $212.56   13.629%   $241.5298   $241.53   $241.55   $241.50  
  Purchase #3 $81.61   12.261%   $91.6162   $91.62   $91.60   $91.60  
  Purchase #4 $147.66   7.327%   $158.479   $158.48   $158.50   $158.50  
  Purchase #5 $162.81   6.786%   $173.8583   $173.86   $173.85   $173.90  
  Purchase #6 $15.50   9.759%   $17.0126   $17.01   $17.00   $17.00  
  Purchase #7 $18.49   5.130%   $19.4385   $19.44   $19.45   $19.40  
  7 purchase totals = $824.98       $904.2248   $904.23   $904.25   $904.20