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	$94.45	5.472%	$99.6183	$99.62	$99.60	$99.60
Purchase #2	$215.95	10.218%	$238.0158	$238.02	$238.00	$238.00
Purchase #3	$139.43	11.354%	$155.2609	$155.26	$155.25	$155.30
Purchase #4	$55.45	11.733%	$61.9559	$61.96	$61.95	$62.00
Purchase #5	$191.39	9.652%	$209.863	$209.86	$209.85	$209.90
Purchase #6	$235.33	3.279%	$243.0465	$243.05	$243.05	$243.00
Purchase #7	$117.65	11.404%	$131.0668	$131.07	$131.05	$131.10
7 purchase totals =	$1,049.65		$1,138.8272	$1,138.84	$1,138.75	$1,138.90