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	$161.31	9.841%	$177.1845	$177.18	$177.20	$177.20
Purchase #2	$76.26	11.472%	$85.0085	$85.01	$85.00	$85.00
Purchase #3	$77.98	9.431%	$85.3343	$85.33	$85.35	$85.30
Purchase #4	$125.86	12.303%	$141.3446	$141.34	$141.35	$141.30
Purchase #5	$155.48	4.245%	$162.0801	$162.08	$162.10	$162.10
Purchase #6	$91.93	8.158%	$99.4296	$99.43	$99.45	$99.40
Purchase #7	$207.54	7.188%	$222.458	$222.46	$222.45	$222.50
7 purchase totals =	$896.36		$972.8396	$972.83	$972.90	$972.80