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	$235.50	12.419%	$264.7467	$264.75	$264.75	$264.70
Purchase #2	$142.57	8.180%	$154.2322	$154.23	$154.25	$154.20
Purchase #3	$210.53	9.193%	$229.884	$229.88	$229.90	$229.90
Purchase #4	$178.26	5.165%	$187.4671	$187.47	$187.45	$187.50
Purchase #5	$231.37	12.116%	$259.4028	$259.40	$259.40	$259.40
Purchase #6	$84.33	6.213%	$89.5694	$89.57	$89.55	$89.60
Purchase #7	$45.78	5.589%	$48.3386	$48.34	$48.35	$48.30
7 purchase totals =	$1,128.34		$1,233.6408	$1,233.64	$1,233.65	$1,233.60