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 $71.82   10.748%   $79.5392   $79.54   $79.55   $79.50  
  Purchase #2 $110.27   7.672%   $118.7299   $118.73   $118.75   $118.70  
  Purchase #3 $200.53   6.522%   $213.6086   $213.61   $213.60   $213.60  
  Purchase #4 $108.40   10.280%   $119.5435   $119.54   $119.55   $119.50  
  Purchase #5 $165.29   6.269%   $175.652   $175.65   $175.65   $175.70  
  Purchase #6 $227.49   11.207%   $252.9848   $252.98   $253.00   $253.00  
  Purchase #7 $23.86   8.369%   $25.8568   $25.86   $25.85   $25.90  
  7 purchase totals = $907.66       $985.9148   $985.91   $985.95   $985.90