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	$120.36	6.130%	$127.7381	$127.74	$127.75	$127.70
Purchase #2	$181.31	5.572%	$191.4126	$191.41	$191.40	$191.40
Purchase #3	$151.41	3.680%	$156.9819	$156.98	$157.00	$157.00
Purchase #4	$191.82	11.756%	$214.3704	$214.37	$214.35	$214.40
Purchase #5	$82.64	13.862%	$94.0956	$94.10	$94.10	$94.10
Purchase #6	$85.39	5.813%	$90.3537	$90.35	$90.35	$90.40
Purchase #7	$102.46	10.289%	$113.0021	$113.00	$113.00	$113.00
7 purchase totals =	$915.39		$987.9544	$987.95	$987.95	$988.00