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 $68.49   6.665%   $73.0549   $73.05   $73.05   $73.10  
  Purchase #2 $18.88   5.327%   $19.8857   $19.89   $19.90   $19.90  
  Purchase #3 $68.54   7.422%   $73.627   $73.63   $73.65   $73.60  
  Purchase #4 $40.28   6.765%   $43.0049   $43.00   $43.00   $43.00  
  Purchase #5 $129.56   13.838%   $147.4885   $147.49   $147.50   $147.50  
  Purchase #6 $243.51   8.151%   $263.3585   $263.36   $263.35   $263.40  
  Purchase #7 $49.92   8.211%   $54.0189   $54.02   $54.00   $54.00  
  7 purchase totals = $619.18       $674.4384   $674.44   $674.45   $674.50