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	$84.96	7.561%	$91.3838	$91.38	$91.40	$91.40
Purchase #2	$87.67	5.118%	$92.157	$92.16	$92.15	$92.20
Purchase #3	$144.96	11.503%	$161.6347	$161.63	$161.65	$161.60
Purchase #4	$109.37	12.577%	$123.1255	$123.13	$123.15	$123.10
Purchase #5	$49.51	13.630%	$56.2582	$56.26	$56.25	$56.30
Purchase #6	$188.27	12.194%	$211.2276	$211.23	$211.25	$211.20
Purchase #7	$76.56	7.689%	$82.4467	$82.45	$82.45	$82.40
7 purchase totals =	$741.30		$818.2335	$818.24	$818.30	$818.20