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	$73.44	12.582%	$82.6802	$82.68	$82.70	$82.70
Purchase #2	$211.76	5.507%	$223.4216	$223.42	$223.40	$223.40
Purchase #3	$127.63	4.237%	$133.0377	$133.04	$133.05	$133.00
Purchase #4	$105.37	3.599%	$109.1623	$109.16	$109.15	$109.20
Purchase #5	$96.72	4.299%	$100.878	$100.88	$100.90	$100.90
Purchase #6	$40.31	4.856%	$42.2675	$42.27	$42.25	$42.30
Purchase #7	$55.50	5.524%	$58.5658	$58.57	$58.55	$58.60
7 purchase totals =	$710.73		$750.0131	$750.02	$750.00	$750.10