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 $62.89   11.364%   $70.0368   $70.04   $70.05   $70.00  
  Purchase #2 $33.29   8.262%   $36.0404   $36.04   $36.05   $36.00  
  Purchase #3 $219.54   10.522%   $242.64   $242.64   $242.65   $242.60  
  Purchase #4 $132.79   3.798%   $137.8334   $137.83   $137.85   $137.80  
  Purchase #5 $133.87   11.353%   $149.0683   $149.07   $149.05   $149.10  
  Purchase #6 $237.92   12.355%   $267.315   $267.32   $267.30   $267.30  
  Purchase #7 $215.36   12.462%   $242.1982   $242.20   $242.20   $242.20  
  7 purchase totals = $1,035.66       $1,145.1321   $1,145.14   $1,145.15   $1,145.00