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	$23.72	13.334%	$26.8828	$26.88	$26.90	$26.90
Purchase #2	$89.89	12.102%	$100.7685	$100.77	$100.75	$100.80
Purchase #3	$89.42	5.764%	$94.5742	$94.57	$94.55	$94.60
Purchase #4	$177.72	4.413%	$185.5628	$185.56	$185.55	$185.60
Purchase #5	$10.27	13.488%	$11.6552	$11.66	$11.65	$11.70
Purchase #6	$90.43	12.221%	$101.4815	$101.48	$101.50	$101.50
Purchase #7	$209.44	7.764%	$225.7009	$225.70	$225.70	$225.70
7 purchase totals =	$690.89		$746.6259	$746.62	$746.60	$746.80