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	$140.36	11.543%	$156.5618	$156.56	$156.55	$156.60
Purchase #2	$221.94	8.352%	$240.4764	$240.48	$240.50	$240.50
Purchase #3	$135.76	8.154%	$146.8299	$146.83	$146.85	$146.80
Purchase #4	$149.48	11.225%	$166.2591	$166.26	$166.25	$166.30
Purchase #5	$225.83	10.753%	$250.1135	$250.11	$250.10	$250.10
Purchase #6	$122.81	6.597%	$130.9118	$130.91	$130.90	$130.90
Purchase #7	$230.78	10.761%	$255.6142	$255.61	$255.60	$255.60
7 purchase totals =	$1,226.96		$1,346.7667	$1,346.76	$1,346.75	$1,346.80