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	$37.92	10.653%	$41.9596	$41.96	$41.95	$42.00
Purchase #2	$167.36	12.384%	$188.0859	$188.09	$188.10	$188.10
Purchase #3	$209.81	7.511%	$225.5688	$225.57	$225.55	$225.60
Purchase #4	$247.39	7.730%	$266.5132	$266.51	$266.50	$266.50
Purchase #5	$157.73	6.840%	$168.5187	$168.52	$168.50	$168.50
Purchase #6	$204.32	6.559%	$217.7213	$217.72	$217.70	$217.70
Purchase #7	$137.90	6.843%	$147.3365	$147.34	$147.35	$147.30
7 purchase totals =	$1,162.43		$1,255.7040	$1,255.71	$1,255.65	$1,255.70