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	$176.55	6.653%	$188.2959	$188.30	$188.30	$188.30
Purchase #2	$130.79	7.461%	$140.5482	$140.55	$140.55	$140.50
Purchase #3	$199.26	5.358%	$209.9364	$209.94	$209.95	$209.90
Purchase #4	$55.36	11.391%	$61.6661	$61.67	$61.65	$61.70
Purchase #5	$33.87	10.670%	$37.4839	$37.48	$37.50	$37.50
Purchase #6	$29.89	5.371%	$31.4954	$31.50	$31.50	$31.50
Purchase #7	$234.74	13.185%	$265.6905	$265.69	$265.70	$265.70
7 purchase totals =	$860.46		$935.1164	$935.13	$935.15	$935.10