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 $158.68   11.442%   $176.8362   $176.84   $176.85   $176.80  
  Purchase #2 $150.65   4.165%   $156.9246   $156.92   $156.90   $156.90  
  Purchase #3 $44.36   12.166%   $49.7568   $49.76   $49.75   $49.80  
  Purchase #4 $22.38   7.661%   $24.0945   $24.09   $24.10   $24.10  
  Purchase #5 $65.92   3.524%   $68.243   $68.24   $68.25   $68.20  
  Purchase #6 $196.82   8.555%   $213.658   $213.66   $213.65   $213.70  
  Purchase #7 $64.31   10.429%   $71.0169   $71.02   $71.00   $71.00  
  7 purchase totals = $703.12       $760.5300   $760.53   $760.50   $760.50