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	$24.62	12.774%	$27.765	$27.77	$27.75	$27.80
Purchase #2	$60.64	10.192%	$66.8204	$66.82	$66.80	$66.80
Purchase #3	$46.86	7.131%	$50.2016	$50.20	$50.20	$50.20
Purchase #4	$36.42	5.148%	$38.2949	$38.29	$38.30	$38.30
Purchase #5	$147.78	11.768%	$165.1708	$165.17	$165.15	$165.20
Purchase #6	$52.66	7.131%	$56.4152	$56.42	$56.40	$56.40
Purchase #7	$86.89	3.490%	$89.9225	$89.92	$89.90	$89.90
7 purchase totals =	$455.87		$494.5904	$494.59	$494.50	$494.60