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	$127.74	4.613%	$133.6326	$133.63	$133.65	$133.60
Purchase #2	$210.43	5.676%	$222.374	$222.37	$222.35	$222.40
Purchase #3	$35.62	13.632%	$40.4757	$40.48	$40.50	$40.50
Purchase #4	$9.96	8.192%	$10.7759	$10.78	$10.80	$10.80
Purchase #5	$133.27	5.842%	$141.0556	$141.06	$141.05	$141.10
Purchase #6	$89.39	4.761%	$93.6459	$93.65	$93.65	$93.60
Purchase #7	$172.61	13.475%	$195.8692	$195.87	$195.85	$195.90
7 purchase totals =	$779.02		$837.8289	$837.84	$837.85	$837.90