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	$38.52	5.488%	$40.634	$40.63	$40.65	$40.60
Purchase #2	$247.53	6.399%	$263.3694	$263.37	$263.35	$263.40
Purchase #3	$222.56	8.465%	$241.3997	$241.40	$241.40	$241.40
Purchase #4	$246.64	7.103%	$264.1588	$264.16	$264.15	$264.20
Purchase #5	$164.97	3.580%	$170.8759	$170.88	$170.90	$170.90
Purchase #6	$225.85	8.873%	$245.8897	$245.89	$245.90	$245.90
Purchase #7	$57.39	7.758%	$61.8423	$61.84	$61.85	$61.80
7 purchase totals =	$1,203.46		$1,288.1698	$1,288.17	$1,288.20	$1,288.20