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	$131.88	3.197%	$136.0962	$136.10	$136.10	$136.10
Purchase #2	$123.48	13.640%	$140.3227	$140.32	$140.30	$140.30
Purchase #3	$103.30	7.765%	$111.3212	$111.32	$111.30	$111.30
Purchase #4	$21.34	7.721%	$22.9877	$22.99	$23.00	$23.00
Purchase #5	$175.98	7.139%	$188.5432	$188.54	$188.55	$188.50
Purchase #6	$34.80	7.766%	$37.5026	$37.50	$37.50	$37.50
Purchase #7	$98.51	5.328%	$103.7586	$103.76	$103.75	$103.80
7 purchase totals =	$689.29		$740.5322	$740.53	$740.50	$740.50