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	$226.90	6.843%	$242.4268	$242.43	$242.45	$242.40
Purchase #2	$97.53	3.676%	$101.1152	$101.12	$101.10	$101.10
Purchase #3	$80.38	10.763%	$89.0313	$89.03	$89.05	$89.00
Purchase #4	$9.32	13.151%	$10.5457	$10.55	$10.55	$10.50
Purchase #5	$18.34	6.221%	$19.4809	$19.48	$19.50	$19.50
Purchase #6	$167.38	8.654%	$181.8651	$181.87	$181.85	$181.90
Purchase #7	$140.80	10.557%	$155.6643	$155.66	$155.65	$155.70
7 purchase totals =	$740.65		$800.1293	$800.14	$800.15	$800.10