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	$78.99	8.596%	$85.78	$85.78	$85.80	$85.80
Purchase #2	$178.31	7.809%	$192.2342	$192.23	$192.25	$192.20
Purchase #3	$216.61	6.204%	$230.0485	$230.05	$230.05	$230.00
Purchase #4	$71.82	12.159%	$80.5526	$80.55	$80.55	$80.60
Purchase #5	$57.61	13.125%	$65.1713	$65.17	$65.15	$65.20
Purchase #6	$168.53	10.159%	$185.651	$185.65	$185.65	$185.70
Purchase #7	$89.33	12.333%	$100.3471	$100.35	$100.35	$100.30
7 purchase totals =	$861.20		$939.7847	$939.78	$939.80	$939.80