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	$52.48	13.348%	$59.485	$59.49	$59.50	$59.50
Purchase #2	$163.90	10.562%	$181.2111	$181.21	$181.20	$181.20
Purchase #3	$243.38	8.735%	$264.6392	$264.64	$264.65	$264.60
Purchase #4	$212.53	5.492%	$224.2021	$224.20	$224.20	$224.20
Purchase #5	$20.99	6.395%	$22.3323	$22.33	$22.35	$22.30
Purchase #6	$107.35	3.672%	$111.2919	$111.29	$111.30	$111.30
Purchase #7	$134.92	3.652%	$139.8473	$139.85	$139.85	$139.80
7 purchase totals =	$935.55		$1,003.0089	$1,003.01	$1,003.05	$1,002.90