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	$228.47	12.115%	$256.1491	$256.15	$256.15	$256.10
Purchase #2	$168.76	9.726%	$185.1736	$185.17	$185.15	$185.20
Purchase #3	$101.89	8.352%	$110.3999	$110.40	$110.40	$110.40
Purchase #4	$113.54	6.367%	$120.7691	$120.77	$120.75	$120.80
Purchase #5	$141.74	4.314%	$147.8547	$147.85	$147.85	$147.90
Purchase #6	$52.46	3.116%	$54.0947	$54.09	$54.10	$54.10
Purchase #7	$18.32	4.230%	$19.0949	$19.09	$19.10	$19.10
7 purchase totals =	$825.18		$893.5360	$893.52	$893.50	$893.60