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	$55.51	6.501%	$59.1187	$59.12	$59.10	$59.10
Purchase #2	$29.82	11.510%	$33.2523	$33.25	$33.25	$33.30
Purchase #3	$22.37	8.873%	$24.3549	$24.35	$24.35	$24.40
Purchase #4	$159.81	9.674%	$175.27	$175.27	$175.25	$175.30
Purchase #5	$217.34	11.544%	$242.4297	$242.43	$242.45	$242.40
Purchase #6	$245.51	8.137%	$265.4871	$265.49	$265.50	$265.50
Purchase #7	$166.85	8.637%	$181.2608	$181.26	$181.25	$181.30
7 purchase totals =	$897.21		$981.1735	$981.17	$981.15	$981.30