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	$34.83	7.144%	$37.3183	$37.32	$37.30	$37.30
Purchase #2	$55.26	3.342%	$57.1068	$57.11	$57.10	$57.10
Purchase #3	$143.78	6.393%	$152.9719	$152.97	$152.95	$153.00
Purchase #4	$182.99	7.407%	$196.5441	$196.54	$196.55	$196.50
Purchase #5	$130.67	12.112%	$146.4968	$146.50	$146.50	$146.50
Purchase #6	$96.49	13.514%	$109.5297	$109.53	$109.55	$109.50
Purchase #7	$133.89	10.666%	$148.1707	$148.17	$148.15	$148.20
7 purchase totals =	$777.91		$848.1383	$848.14	$848.10	$848.10