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	$155.77	6.440%	$165.8016	$165.80	$165.80	$165.80
Purchase #2	$102.74	6.187%	$109.0965	$109.10	$109.10	$109.10
Purchase #3	$26.33	10.717%	$29.1518	$29.15	$29.15	$29.20
Purchase #4	$181.88	6.850%	$194.3388	$194.34	$194.35	$194.30
Purchase #5	$167.40	6.616%	$178.4752	$178.48	$178.50	$178.50
Purchase #6	$78.27	6.745%	$83.5493	$83.55	$83.55	$83.50
Purchase #7	$37.86	3.483%	$39.1787	$39.18	$39.20	$39.20
7 purchase totals =	$750.25		$799.5919	$799.60	$799.65	$799.60