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	$211.78	6.288%	$225.0967	$225.10	$225.10	$225.10
Purchase #2	$109.52	12.834%	$123.5758	$123.58	$123.60	$123.60
Purchase #3	$161.96	3.501%	$167.6302	$167.63	$167.65	$167.60
Purchase #4	$162.69	10.157%	$179.2144	$179.21	$179.20	$179.20
Purchase #5	$12.71	4.717%	$13.3095	$13.31	$13.30	$13.30
Purchase #6	$137.56	3.144%	$141.8849	$141.88	$141.90	$141.90
Purchase #7	$61.58	7.355%	$66.1092	$66.11	$66.10	$66.10
7 purchase totals =	$857.80		$916.8207	$916.82	$916.85	$916.80