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	$31.58	4.406%	$32.9714	$32.97	$32.95	$33.00
Purchase #2	$151.84	6.179%	$161.2222	$161.22	$161.20	$161.20
Purchase #3	$6.34	3.733%	$6.5767	$6.58	$6.60	$6.60
Purchase #4	$17.74	3.817%	$18.4171	$18.42	$18.40	$18.40
Purchase #5	$55.86	5.716%	$59.053	$59.05	$59.05	$59.10
Purchase #6	$222.50	12.265%	$249.7896	$249.79	$249.80	$249.80
Purchase #7	$78.74	13.751%	$89.5675	$89.57	$89.55	$89.60
7 purchase totals =	$564.60		$617.5975	$617.60	$617.55	$617.70