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	$31.69	3.682%	$32.8568	$32.86	$32.85	$32.90
Purchase #2	$37.53	12.401%	$42.1841	$42.18	$42.20	$42.20
Purchase #3	$53.96	11.861%	$60.3602	$60.36	$60.35	$60.40
Purchase #4	$197.44	12.691%	$222.4971	$222.50	$222.50	$222.50
Purchase #5	$208.39	7.132%	$223.2524	$223.25	$223.25	$223.30
Purchase #6	$43.58	12.348%	$48.9613	$48.96	$48.95	$49.00
Purchase #7	$156.98	11.764%	$175.4471	$175.45	$175.45	$175.40
7 purchase totals =	$729.57		$805.5590	$805.56	$805.55	$805.70