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 $69.95   4.717%   $73.2495   $73.25   $73.25   $73.20  
  Purchase #2 $190.75   7.236%   $204.5527   $204.55   $204.55   $204.60  
  Purchase #3 $127.76   5.630%   $134.9529   $134.95   $134.95   $135.00  
  Purchase #4 $227.61   7.111%   $243.7953   $243.80   $243.80   $243.80  
  Purchase #5 $54.39   5.654%   $57.4652   $57.47   $57.45   $57.50  
  Purchase #6 $65.44   6.664%   $69.8009   $69.80   $69.80   $69.80  
  Purchase #7 $85.25   12.572%   $95.9676   $95.97   $95.95   $96.00  
  7 purchase totals = $821.15       $879.7841   $879.79   $879.75   $879.90