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	$28.86	11.305%	$32.1226	$32.12	$32.10	$32.10
Purchase #2	$200.37	11.382%	$223.1761	$223.18	$223.20	$223.20
Purchase #3	$11.45	11.688%	$12.7883	$12.79	$12.80	$12.80
Purchase #4	$30.32	9.205%	$33.111	$33.11	$33.10	$33.10
Purchase #5	$83.62	6.842%	$89.3413	$89.34	$89.35	$89.30
Purchase #6	$125.32	13.516%	$142.2583	$142.26	$142.25	$142.30
Purchase #7	$124.39	3.858%	$129.189	$129.19	$129.20	$129.20
7 purchase totals =	$604.33		$661.9866	$661.99	$662.00	$662.00