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	$139.30	12.549%	$156.7808	$156.78	$156.80	$156.80
Purchase #2	$23.52	4.792%	$24.6471	$24.65	$24.65	$24.60
Purchase #3	$249.76	9.563%	$273.6445	$273.64	$273.65	$273.60
Purchase #4	$243.66	12.223%	$273.4426	$273.44	$273.45	$273.40
Purchase #5	$164.38	10.437%	$181.5363	$181.54	$181.55	$181.50
Purchase #6	$118.25	5.259%	$124.4688	$124.47	$124.45	$124.50
Purchase #7	$50.56	9.830%	$55.53	$55.53	$55.55	$55.50
7 purchase totals =	$989.43		$1,090.0501	$1,090.05	$1,090.10	$1,089.90