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	$118.33	13.421%	$134.2111	$134.21	$134.20	$134.20
Purchase #2	$82.36	8.735%	$89.5541	$89.55	$89.55	$89.60
Purchase #3	$82.29	11.165%	$91.4777	$91.48	$91.50	$91.50
Purchase #4	$151.88	6.234%	$161.3482	$161.35	$161.35	$161.30
Purchase #5	$131.63	11.356%	$146.5779	$146.58	$146.60	$146.60
Purchase #6	$139.93	7.183%	$149.9812	$149.98	$150.00	$150.00
Purchase #7	$88.30	10.295%	$97.3905	$97.39	$97.40	$97.40
7 purchase totals =	$794.72		$870.5407	$870.54	$870.60	$870.60