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	$250.43	11.460%	$279.1293	$279.13	$279.15	$279.10
Purchase #2	$53.46	8.792%	$58.1602	$58.16	$58.15	$58.20
Purchase #3	$82.61	5.458%	$87.1189	$87.12	$87.10	$87.10
Purchase #4	$52.63	10.123%	$57.9577	$57.96	$57.95	$58.00
Purchase #5	$80.47	11.230%	$89.5068	$89.51	$89.50	$89.50
Purchase #6	$159.81	3.285%	$165.0598	$165.06	$165.05	$165.10
Purchase #7	$7.46	6.547%	$7.9484	$7.95	$7.95	$7.90
7 purchase totals =	$686.87		$744.8811	$744.89	$744.85	$744.90