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	$203.90	3.754%	$211.5544	$211.55	$211.55	$211.60
Purchase #2	$112.63	6.363%	$119.7966	$119.80	$119.80	$119.80
Purchase #3	$20.37	6.455%	$21.6849	$21.68	$21.70	$21.70
Purchase #4	$238.25	3.704%	$247.0748	$247.07	$247.05	$247.10
Purchase #5	$80.91	10.275%	$89.2235	$89.22	$89.20	$89.20
Purchase #6	$243.66	8.714%	$264.8925	$264.89	$264.90	$264.90
Purchase #7	$26.35	3.693%	$27.3231	$27.32	$27.30	$27.30
7 purchase totals =	$926.07		$981.5498	$981.53	$981.50	$981.60