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 $192.60   11.793%   $215.3133   $215.31   $215.30   $215.30  
  Purchase #2 $230.64   8.484%   $250.2075   $250.21   $250.20   $250.20  
  Purchase #3 $250.65   8.839%   $272.805   $272.81   $272.80   $272.80  
  Purchase #4 $190.34   12.397%   $213.9364   $213.94   $213.95   $213.90  
  Purchase #5 $196.34   5.766%   $207.661   $207.66   $207.65   $207.70  
  Purchase #6 $149.45   6.553%   $159.2435   $159.24   $159.25   $159.20  
  Purchase #7 $133.44   6.430%   $142.0202   $142.02   $142.00   $142.00  
  7 purchase totals = $1,343.46       $1,461.1869   $1,461.19   $1,461.15   $1,461.10