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	$229.95	12.356%	$258.3626	$258.36	$258.35	$258.40
Purchase #2	$117.50	3.535%	$121.6536	$121.65	$121.65	$121.70
Purchase #3	$25.59	10.573%	$28.2956	$28.30	$28.30	$28.30
Purchase #4	$82.74	9.802%	$90.8502	$90.85	$90.85	$90.90
Purchase #5	$127.48	11.223%	$141.7871	$141.79	$141.80	$141.80
Purchase #6	$140.84	6.871%	$150.5171	$150.52	$150.50	$150.50
Purchase #7	$12.46	13.251%	$14.1111	$14.11	$14.10	$14.10
7 purchase totals =	$736.56		$805.5773	$805.58	$805.55	$805.70