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	$23.56	12.846%	$26.5865	$26.59	$26.60	$26.60
Purchase #2	$98.53	12.357%	$110.7054	$110.71	$110.70	$110.70
Purchase #3	$74.49	11.350%	$82.9446	$82.94	$82.95	$82.90
Purchase #4	$150.89	9.632%	$165.4237	$165.42	$165.40	$165.40
Purchase #5	$201.49	6.319%	$214.2222	$214.22	$214.20	$214.20
Purchase #6	$53.37	11.685%	$59.6063	$59.61	$59.60	$59.60
Purchase #7	$59.47	3.810%	$61.7358	$61.74	$61.75	$61.70
7 purchase totals =	$661.80		$721.2245	$721.23	$721.20	$721.10