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	$27.57	4.742%	$28.8774	$28.88	$28.90	$28.90
Purchase #2	$122.34	4.107%	$127.3645	$127.36	$127.35	$127.40
Purchase #3	$135.45	8.804%	$147.375	$147.38	$147.40	$147.40
Purchase #4	$49.29	4.346%	$51.4321	$51.43	$51.45	$51.40
Purchase #5	$61.57	10.188%	$67.8428	$67.84	$67.85	$67.80
Purchase #6	$25.43	11.297%	$28.3028	$28.30	$28.30	$28.30
Purchase #7	$59.35	4.511%	$62.0273	$62.03	$62.05	$62.00
7 purchase totals =	$481.00		$513.2219	$513.22	$513.30	$513.20