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	$41.54	12.635%	$46.7886	$46.79	$46.80	$46.80
Purchase #2	$241.80	11.442%	$269.4668	$269.47	$269.45	$269.50
Purchase #3	$150.33	7.110%	$161.0185	$161.02	$161.00	$161.00
Purchase #4	$131.30	6.547%	$139.8962	$139.90	$139.90	$139.90
Purchase #5	$39.86	4.620%	$41.7015	$41.70	$41.70	$41.70
Purchase #6	$50.56	6.250%	$53.72	$53.72	$53.70	$53.70
Purchase #7	$79.39	12.131%	$89.0208	$89.02	$89.00	$89.00
7 purchase totals =	$734.78		$801.6124	$801.62	$801.55	$801.60