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	$6.67	6.701%	$7.117	$7.12	$7.10	$7.10
Purchase #2	$217.84	9.425%	$238.3714	$238.37	$238.35	$238.40
Purchase #3	$128.59	13.827%	$146.3701	$146.37	$146.35	$146.40
Purchase #4	$175.62	3.339%	$181.484	$181.48	$181.50	$181.50
Purchase #5	$77.58	6.601%	$82.7011	$82.70	$82.70	$82.70
Purchase #6	$100.77	11.275%	$112.1318	$112.13	$112.15	$112.10
Purchase #7	$63.27	3.403%	$65.4231	$65.42	$65.40	$65.40
7 purchase totals =	$770.34		$833.5985	$833.59	$833.55	$833.60