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	$179.78	4.753%	$188.3249	$188.32	$188.30	$188.30
Purchase #2	$32.27	8.797%	$35.1088	$35.11	$35.10	$35.10
Purchase #3	$55.81	12.748%	$62.9247	$62.92	$62.90	$62.90
Purchase #4	$150.29	6.299%	$159.7568	$159.76	$159.75	$159.80
Purchase #5	$198.42	5.600%	$209.5315	$209.53	$209.55	$209.50
Purchase #6	$141.80	10.378%	$156.516	$156.52	$156.50	$156.50
Purchase #7	$55.28	7.201%	$59.2607	$59.26	$59.25	$59.30
7 purchase totals =	$813.65		$871.4234	$871.42	$871.35	$871.40