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	$139.73	5.111%	$146.8716	$146.87	$146.85	$146.90
Purchase #2	$64.47	3.166%	$66.5111	$66.51	$66.50	$66.50
Purchase #3	$209.33	13.797%	$238.2113	$238.21	$238.20	$238.20
Purchase #4	$30.46	11.506%	$33.9647	$33.96	$33.95	$34.00
Purchase #5	$186.37	6.796%	$199.0357	$199.04	$199.05	$199.00
Purchase #6	$49.92	12.201%	$56.0107	$56.01	$56.00	$56.00
Purchase #7	$184.29	6.657%	$196.5582	$196.56	$196.55	$196.60
7 purchase totals =	$864.57		$937.1633	$937.16	$937.10	$937.20