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	$64.88	5.586%	$68.5042	$68.50	$68.50	$68.50
Purchase #2	$244.56	8.364%	$265.015	$265.02	$265.00	$265.00
Purchase #3	$99.77	10.645%	$110.3905	$110.39	$110.40	$110.40
Purchase #4	$91.72	4.119%	$95.4979	$95.50	$95.50	$95.50
Purchase #5	$206.78	12.828%	$233.3057	$233.31	$233.30	$233.30
Purchase #6	$84.51	5.586%	$89.2307	$89.23	$89.25	$89.20
Purchase #7	$32.92	10.282%	$36.3048	$36.30	$36.30	$36.30
7 purchase totals =	$825.14		$898.2488	$898.25	$898.25	$898.20