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 $62.33   12.672%   $70.2285   $70.23   $70.25   $70.20  
  Purchase #2 $106.44   11.820%   $119.0212   $119.02   $119.00   $119.00  
  Purchase #3 $217.88   5.249%   $229.3165   $229.32   $229.30   $229.30  
  Purchase #4 $63.53   8.240%   $68.7649   $68.76   $68.75   $68.80  
  Purchase #5 $173.40   6.655%   $184.9398   $184.94   $184.95   $184.90  
  Purchase #6 $90.88   11.750%   $101.5584   $101.56   $101.55   $101.60  
  Purchase #7 $230.86   5.463%   $243.4719   $243.47   $243.45   $243.50  
  7 purchase totals = $945.32       $1,017.3012   $1,017.30   $1,017.25   $1,017.30