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	$55.61	6.436%	$59.1891	$59.19	$59.20	$59.20
Purchase #2	$78.58	9.483%	$86.0317	$86.03	$86.05	$86.00
Purchase #3	$58.39	5.287%	$61.4771	$61.48	$61.50	$61.50
Purchase #4	$15.74	10.164%	$17.3398	$17.34	$17.35	$17.30
Purchase #5	$149.73	6.789%	$159.8952	$159.90	$159.90	$159.90
Purchase #6	$44.84	5.742%	$47.4147	$47.41	$47.40	$47.40
Purchase #7	$128.92	10.706%	$142.7222	$142.72	$142.70	$142.70
7 purchase totals =	$531.81		$574.0698	$574.07	$574.10	$574.00