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	$124.39	4.412%	$129.8781	$129.88	$129.90	$129.90
Purchase #2	$203.34	9.375%	$222.4031	$222.40	$222.40	$222.40
Purchase #3	$211.95	5.523%	$223.656	$223.66	$223.65	$223.70
Purchase #4	$69.80	12.248%	$78.3491	$78.35	$78.35	$78.30
Purchase #5	$17.84	12.501%	$20.0702	$20.07	$20.05	$20.10
Purchase #6	$86.57	11.781%	$96.7688	$96.77	$96.75	$96.80
Purchase #7	$179.63	11.548%	$200.3737	$200.37	$200.35	$200.40
7 purchase totals =	$893.52		$971.4990	$971.50	$971.45	$971.60