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	$234.31	8.108%	$253.3079	$253.31	$253.30	$253.30
Purchase #2	$58.70	13.780%	$66.7889	$66.79	$66.80	$66.80
Purchase #3	$120.69	13.742%	$137.2752	$137.28	$137.30	$137.30
Purchase #4	$50.46	11.724%	$56.3759	$56.38	$56.40	$56.40
Purchase #5	$233.82	5.833%	$247.4587	$247.46	$247.45	$247.50
Purchase #6	$20.53	11.695%	$22.931	$22.93	$22.95	$22.90
Purchase #7	$241.50	6.226%	$256.5358	$256.54	$256.55	$256.50
7 purchase totals =	$960.01		$1,040.6734	$1,040.69	$1,040.75	$1,040.70