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	$247.88	8.355%	$268.5904	$268.59	$268.60	$268.60
Purchase #2	$225.88	10.694%	$250.0356	$250.04	$250.05	$250.00
Purchase #3	$47.76	9.597%	$52.3435	$52.34	$52.35	$52.30
Purchase #4	$113.50	8.662%	$123.3314	$123.33	$123.35	$123.30
Purchase #5	$242.41	5.438%	$255.5923	$255.59	$255.60	$255.60
Purchase #6	$234.35	12.809%	$264.3679	$264.37	$264.35	$264.40
Purchase #7	$124.64	13.733%	$141.7568	$141.76	$141.75	$141.80
7 purchase totals =	$1,236.42		$1,356.0179	$1,356.02	$1,356.05	$1,356.00