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	$39.47	6.534%	$42.049	$42.05	$42.05	$42.00
Purchase #2	$34.77	4.190%	$36.2269	$36.23	$36.25	$36.20
Purchase #3	$82.91	8.140%	$89.6589	$89.66	$89.65	$89.70
Purchase #4	$137.37	12.865%	$155.0427	$155.04	$155.05	$155.00
Purchase #5	$145.29	4.434%	$151.7322	$151.73	$151.75	$151.70
Purchase #6	$16.44	10.468%	$18.1609	$18.16	$18.15	$18.20
Purchase #7	$104.47	6.177%	$110.9231	$110.92	$110.90	$110.90
7 purchase totals =	$560.72		$603.7937	$603.79	$603.80	$603.70