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	$131.69	3.388%	$136.1517	$136.15	$136.15	$136.20
Purchase #2	$81.67	9.758%	$89.6394	$89.64	$89.65	$89.60
Purchase #3	$55.50	11.664%	$61.9735	$61.97	$61.95	$62.00
Purchase #4	$80.73	5.749%	$85.3712	$85.37	$85.35	$85.40
Purchase #5	$225.64	9.782%	$247.7121	$247.71	$247.70	$247.70
Purchase #6	$88.27	3.494%	$91.3542	$91.35	$91.35	$91.40
Purchase #7	$139.72	13.200%	$158.163	$158.16	$158.15	$158.20
7 purchase totals =	$803.22		$870.3651	$870.35	$870.30	$870.50