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	$85.69	5.618%	$90.5041	$90.50	$90.50	$90.50
Purchase #2	$244.50	8.291%	$264.7715	$264.77	$264.75	$264.80
Purchase #3	$99.53	10.649%	$110.1289	$110.13	$110.15	$110.10
Purchase #4	$62.55	13.596%	$71.0543	$71.05	$71.05	$71.10
Purchase #5	$22.89	10.362%	$25.2619	$25.26	$25.25	$25.30
Purchase #6	$96.61	13.576%	$109.7258	$109.73	$109.75	$109.70
Purchase #7	$129.25	11.806%	$144.5093	$144.51	$144.50	$144.50
7 purchase totals =	$741.02		$815.9558	$815.95	$815.95	$816.00