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	$130.37	5.860%	$138.0097	$138.01	$138.00	$138.00
Purchase #2	$161.56	11.243%	$179.7242	$179.72	$179.70	$179.70
Purchase #3	$39.46	11.342%	$43.9356	$43.94	$43.95	$43.90
Purchase #4	$67.30	6.621%	$71.7559	$71.76	$71.75	$71.80
Purchase #5	$192.42	13.832%	$219.0355	$219.04	$219.05	$219.00
Purchase #6	$85.80	10.383%	$94.7086	$94.71	$94.70	$94.70
Purchase #7	$57.86	6.865%	$61.8321	$61.83	$61.85	$61.80
7 purchase totals =	$734.77		$809.0016	$809.01	$809.00	$808.90