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	$178.98	4.702%	$187.3956	$187.40	$187.40	$187.40
Purchase #2	$146.25	6.760%	$156.1365	$156.14	$156.15	$156.10
Purchase #3	$171.54	7.397%	$184.2288	$184.23	$184.25	$184.20
Purchase #4	$111.72	5.267%	$117.6043	$117.60	$117.60	$117.60
Purchase #5	$87.71	4.369%	$91.542	$91.54	$91.55	$91.50
Purchase #6	$79.91	12.485%	$89.8868	$89.89	$89.90	$89.90
Purchase #7	$99.82	10.740%	$110.5407	$110.54	$110.55	$110.50
7 purchase totals =	$875.93		$937.3347	$937.34	$937.40	$937.20