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	$185.89	3.278%	$191.9835	$191.98	$192.00	$192.00
Purchase #2	$56.90	12.738%	$64.1479	$64.15	$64.15	$64.10
Purchase #3	$23.77	11.485%	$26.5	$26.50	$26.50	$26.50
Purchase #4	$140.30	8.229%	$151.8453	$151.85	$151.85	$151.80
Purchase #5	$31.84	4.518%	$33.2785	$33.28	$33.30	$33.30
Purchase #6	$134.38	3.111%	$138.5606	$138.56	$138.55	$138.60
Purchase #7	$78.96	4.848%	$82.788	$82.79	$82.80	$82.80
7 purchase totals =	$652.04		$689.1038	$689.11	$689.15	$689.10