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	$25.56	11.204%	$28.4237	$28.42	$28.40	$28.40
Purchase #2	$185.48	5.256%	$195.2288	$195.23	$195.25	$195.20
Purchase #3	$99.31	5.592%	$104.8634	$104.86	$104.85	$104.90
Purchase #4	$216.95	13.473%	$246.1797	$246.18	$246.20	$246.20
Purchase #5	$113.69	6.834%	$121.4596	$121.46	$121.45	$121.50
Purchase #6	$198.64	12.298%	$223.0687	$223.07	$223.05	$223.10
Purchase #7	$175.27	8.701%	$190.5202	$190.52	$190.50	$190.50
7 purchase totals =	$1,014.90		$1,109.7441	$1,109.74	$1,109.70	$1,109.80