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	$15.58	10.289%	$17.183	$17.18	$17.20	$17.20
Purchase #2	$185.27	6.258%	$196.8642	$196.86	$196.85	$196.90
Purchase #3	$211.36	9.213%	$230.8326	$230.83	$230.85	$230.80
Purchase #4	$216.26	4.339%	$225.6435	$225.64	$225.65	$225.60
Purchase #5	$119.69	9.735%	$131.3418	$131.34	$131.35	$131.30
Purchase #6	$133.54	10.106%	$147.0356	$147.04	$147.05	$147.00
Purchase #7	$171.73	11.502%	$191.4824	$191.48	$191.50	$191.50
7 purchase totals =	$1,053.43		$1,140.3831	$1,140.37	$1,140.45	$1,140.30