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	$36.88	6.389%	$39.2363	$39.24	$39.25	$39.20
Purchase #2	$165.51	13.749%	$188.266	$188.27	$188.25	$188.30
Purchase #3	$189.86	13.607%	$215.6943	$215.69	$215.70	$215.70
Purchase #4	$152.72	4.665%	$159.8444	$159.84	$159.85	$159.80
Purchase #5	$221.45	9.429%	$242.3305	$242.33	$242.35	$242.30
Purchase #6	$146.76	6.220%	$155.8885	$155.89	$155.90	$155.90
Purchase #7	$143.51	11.409%	$159.8831	$159.88	$159.90	$159.90
7 purchase totals =	$1,056.69		$1,161.1431	$1,161.14	$1,161.20	$1,161.10