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 $58.57   3.295%   $60.4999   $60.50   $60.50   $60.50  
  Purchase #2 $235.33   3.121%   $242.6746   $242.67   $242.65   $242.70  
  Purchase #3 $96.70   8.411%   $104.8334   $104.83   $104.85   $104.80  
  Purchase #4 $120.42   13.532%   $136.7152   $136.72   $136.70   $136.70  
  Purchase #5 $32.39   5.423%   $34.1465   $34.15   $34.15   $34.10  
  Purchase #6 $250.25   11.216%   $278.318   $278.32   $278.30   $278.30  
  Purchase #7 $132.60   8.582%   $143.9797   $143.98   $144.00   $144.00  
  7 purchase totals = $926.26       $1,001.1673   $1,001.17   $1,001.15   $1,001.10