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 $77.71   9.760%   $85.2945   $85.29   $85.30   $85.30  
  Purchase #2 $210.64   11.538%   $234.9436   $234.94   $234.95   $234.90  
  Purchase #3 $229.98   6.517%   $244.9678   $244.97   $244.95   $245.00  
  Purchase #4 $108.61   11.661%   $121.275   $121.28   $121.30   $121.30  
  Purchase #5 $184.82   3.846%   $191.9282   $191.93   $191.95   $191.90  
  Purchase #6 $127.99   3.302%   $132.2162   $132.22   $132.20   $132.20  
  Purchase #7 $5.76   9.519%   $6.3083   $6.31   $6.30   $6.30  
  7 purchase totals = $945.51       $1,016.9336   $1,016.94   $1,016.95   $1,016.90