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 $72.99   4.303%   $76.1308   $76.13   $76.15   $76.10  
  Purchase #2 $23.95   13.761%   $27.2458   $27.25   $27.25   $27.20  
  Purchase #3 $58.95   11.412%   $65.6774   $65.68   $65.70   $65.70  
  Purchase #4 $58.35   13.371%   $66.152   $66.15   $66.15   $66.20  
  Purchase #5 $79.64   11.342%   $88.6728   $88.67   $88.65   $88.70  
  Purchase #6 $206.82   3.300%   $213.6451   $213.65   $213.65   $213.60  
  Purchase #7 $192.94   13.368%   $218.7322   $218.73   $218.75   $218.70  
  7 purchase totals = $693.64       $756.2561   $756.26   $756.30   $756.20