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 $217.47   13.583%   $247.009   $247.01   $247.00   $247.00  
  Purchase #2 $87.43   7.540%   $94.0222   $94.02   $94.00   $94.00  
  Purchase #3 $8.68   12.869%   $9.797   $9.80   $9.80   $9.80  
  Purchase #4 $45.71   8.225%   $49.4696   $49.47   $49.45   $49.50  
  Purchase #5 $199.57   4.187%   $207.926   $207.93   $207.95   $207.90  
  Purchase #6 $81.79   3.545%   $84.6895   $84.69   $84.70   $84.70  
  Purchase #7 $200.39   5.507%   $211.4255   $211.43   $211.45   $211.40  
  7 purchase totals = $841.04       $904.3388   $904.35   $904.35   $904.30