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	$215.51	7.341%	$231.3306	$231.33	$231.35	$231.30
Purchase #2	$247.86	3.600%	$256.783	$256.78	$256.80	$256.80
Purchase #3	$157.37	7.362%	$168.9556	$168.96	$168.95	$169.00
Purchase #4	$11.53	8.788%	$12.5433	$12.54	$12.55	$12.50
Purchase #5	$119.57	9.643%	$131.1001	$131.10	$131.10	$131.10
Purchase #6	$20.95	9.356%	$22.9101	$22.91	$22.90	$22.90
Purchase #7	$247.79	6.405%	$263.6609	$263.66	$263.65	$263.70
7 purchase totals =	$1,020.58		$1,087.2836	$1,087.28	$1,087.30	$1,087.30