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	$64.93	3.641%	$67.2941	$67.29	$67.30	$67.30
Purchase #2	$51.54	6.818%	$55.054	$55.05	$55.05	$55.10
Purchase #3	$69.68	3.155%	$71.8784	$71.88	$71.90	$71.90
Purchase #4	$173.39	8.687%	$188.4524	$188.45	$188.45	$188.50
Purchase #5	$171.98	11.207%	$191.2538	$191.25	$191.25	$191.30
Purchase #6	$20.52	6.847%	$21.925	$21.93	$21.95	$21.90
Purchase #7	$221.28	7.547%	$237.98	$237.98	$238.00	$238.00
7 purchase totals =	$773.32		$833.8377	$833.83	$833.90	$834.00