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	$75.94	9.764%	$83.3548	$83.35	$83.35	$83.40
Purchase #2	$164.67	10.806%	$182.4642	$182.46	$182.45	$182.50
Purchase #3	$134.83	13.574%	$153.1318	$153.13	$153.15	$153.10
Purchase #4	$160.33	3.449%	$165.8598	$165.86	$165.85	$165.90
Purchase #5	$167.74	7.601%	$180.4899	$180.49	$180.50	$180.50
Purchase #6	$153.89	8.823%	$167.4677	$167.47	$167.45	$167.50
Purchase #7	$216.33	11.288%	$240.7493	$240.75	$240.75	$240.70
7 purchase totals =	$1,073.73		$1,173.5175	$1,173.51	$1,173.50	$1,173.60