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	$242.91	5.753%	$256.8846	$256.88	$256.90	$256.90
Purchase #2	$91.63	13.806%	$104.2804	$104.28	$104.30	$104.30
Purchase #3	$83.52	6.649%	$89.0732	$89.07	$89.05	$89.10
Purchase #4	$206.41	12.308%	$231.8149	$231.81	$231.80	$231.80
Purchase #5	$63.28	6.291%	$67.2609	$67.26	$67.25	$67.30
Purchase #6	$124.36	10.152%	$136.985	$136.99	$137.00	$137.00
Purchase #7	$159.89	12.421%	$179.7499	$179.75	$179.75	$179.70
7 purchase totals =	$972.00		$1,066.0489	$1,066.04	$1,066.05	$1,066.10