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 $228.53   6.329%   $242.9937   $242.99   $243.00   $243.00  
  Purchase #2 $163.71   12.365%   $183.9527   $183.95   $183.95   $184.00  
  Purchase #3 $221.38   4.229%   $230.7422   $230.74   $230.75   $230.70  
  Purchase #4 $189.71   4.348%   $197.9586   $197.96   $197.95   $198.00  
  Purchase #5 $55.95   10.735%   $61.9562   $61.96   $61.95   $62.00  
  Purchase #6 $220.27   13.354%   $249.6849   $249.68   $249.70   $249.70  
  Purchase #7 $189.48   5.216%   $199.3633   $199.36   $199.35   $199.40  
  7 purchase totals = $1,269.03       $1,366.6516   $1,366.64   $1,366.65   $1,366.80