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	$39.54	10.109%	$43.5371	$43.54	$43.55	$43.50
Purchase #2	$98.44	5.686%	$104.0373	$104.04	$104.05	$104.00
Purchase #3	$64.35	12.404%	$72.332	$72.33	$72.35	$72.30
Purchase #4	$146.48	13.760%	$166.6356	$166.64	$166.65	$166.60
Purchase #5	$39.61	4.366%	$41.3394	$41.34	$41.35	$41.30
Purchase #6	$55.41	8.695%	$60.2279	$60.23	$60.25	$60.20
Purchase #7	$32.72	8.548%	$35.5169	$35.52	$35.50	$35.50
7 purchase totals =	$476.55		$523.6262	$523.64	$523.70	$523.40