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	$31.98	10.655%	$35.3875	$35.39	$35.40	$35.40
Purchase #2	$54.82	8.732%	$59.6069	$59.61	$59.60	$59.60
Purchase #3	$85.69	5.220%	$90.163	$90.16	$90.15	$90.20
Purchase #4	$84.59	7.719%	$91.1195	$91.12	$91.10	$91.10
Purchase #5	$74.63	8.579%	$81.0325	$81.03	$81.05	$81.00
Purchase #6	$83.67	11.798%	$93.5414	$93.54	$93.55	$93.50
Purchase #7	$90.45	13.422%	$102.5902	$102.59	$102.60	$102.60
7 purchase totals =	$505.83		$553.4410	$553.44	$553.45	$553.40