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	$24.48	7.138%	$26.2274	$26.23	$26.25	$26.20
Purchase #2	$122.56	4.268%	$127.7909	$127.79	$127.80	$127.80
Purchase #3	$175.45	7.755%	$189.0561	$189.06	$189.05	$189.10
Purchase #4	$136.80	10.135%	$150.6647	$150.66	$150.65	$150.70
Purchase #5	$175.27	12.345%	$196.9071	$196.91	$196.90	$196.90
Purchase #6	$246.80	11.550%	$275.3054	$275.31	$275.30	$275.30
Purchase #7	$184.42	7.855%	$198.9062	$198.91	$198.90	$198.90
7 purchase totals =	$1,065.78		$1,164.8578	$1,164.87	$1,164.85	$1,164.90