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	$75.36	10.215%	$83.058	$83.06	$83.05	$83.10
Purchase #2	$18.83	11.568%	$21.0083	$21.01	$21.00	$21.00
Purchase #3	$136.45	6.391%	$145.1705	$145.17	$145.15	$145.20
Purchase #4	$22.98	12.390%	$25.8272	$25.83	$25.85	$25.80
Purchase #5	$31.46	6.554%	$33.5219	$33.52	$33.50	$33.50
Purchase #6	$36.30	3.692%	$37.6402	$37.64	$37.65	$37.60
Purchase #7	$58.77	9.504%	$64.3555	$64.36	$64.35	$64.40
7 purchase totals =	$380.15		$410.5816	$410.59	$410.55	$410.60