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	$30.55	5.518%	$32.2357	$32.24	$32.25	$32.20
Purchase #2	$93.47	7.585%	$100.5597	$100.56	$100.55	$100.60
Purchase #3	$85.68	6.833%	$91.5345	$91.53	$91.55	$91.50
Purchase #4	$46.90	5.622%	$49.5367	$49.54	$49.55	$49.50
Purchase #5	$17.26	7.387%	$18.535	$18.54	$18.55	$18.50
Purchase #6	$75.98	8.232%	$82.2347	$82.23	$82.25	$82.20
Purchase #7	$166.49	11.564%	$185.7429	$185.74	$185.75	$185.70
7 purchase totals =	$516.33		$560.3792	$560.38	$560.45	$560.20