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	$243.47	3.220%	$251.3097	$251.31	$251.30	$251.30
Purchase #2	$51.81	11.593%	$57.8163	$57.82	$57.80	$57.80
Purchase #3	$168.97	12.767%	$190.5424	$190.54	$190.55	$190.50
Purchase #4	$131.65	10.245%	$145.1375	$145.14	$145.15	$145.10
Purchase #5	$132.41	11.244%	$147.2982	$147.30	$147.30	$147.30
Purchase #6	$178.74	6.707%	$190.7281	$190.73	$190.75	$190.70
Purchase #7	$227.83	4.689%	$238.5129	$238.51	$238.50	$238.50
7 purchase totals =	$1,134.88		$1,221.3451	$1,221.35	$1,221.35	$1,221.20