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	$39.59	6.633%	$42.216	$42.22	$42.20	$42.20
Purchase #2	$143.76	6.390%	$152.9463	$152.95	$152.95	$152.90
Purchase #3	$179.35	11.751%	$200.4254	$200.43	$200.45	$200.40
Purchase #4	$159.83	3.765%	$165.8476	$165.85	$165.85	$165.80
Purchase #5	$235.58	12.452%	$264.9144	$264.91	$264.90	$264.90
Purchase #6	$197.33	11.634%	$220.2874	$220.29	$220.30	$220.30
Purchase #7	$140.64	7.254%	$150.842	$150.84	$150.85	$150.80
7 purchase totals =	$1,096.08		$1,197.4791	$1,197.49	$1,197.50	$1,197.30