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	$54.54	9.800%	$59.8849	$59.88	$59.90	$59.90
Purchase #2	$77.39	13.663%	$87.9638	$87.96	$87.95	$88.00
Purchase #3	$150.65	9.623%	$165.147	$165.15	$165.15	$165.10
Purchase #4	$89.48	10.739%	$99.0893	$99.09	$99.10	$99.10
Purchase #5	$231.71	6.380%	$246.4931	$246.49	$246.50	$246.50
Purchase #6	$241.25	3.644%	$250.0412	$250.04	$250.05	$250.00
Purchase #7	$60.47	10.220%	$66.65	$66.65	$66.65	$66.70
7 purchase totals =	$905.49		$975.2693	$975.26	$975.30	$975.30