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	$124.86	13.834%	$142.1331	$142.13	$142.15	$142.10
Purchase #2	$243.50	12.414%	$273.7281	$273.73	$273.75	$273.70
Purchase #3	$152.29	10.620%	$168.4632	$168.46	$168.45	$168.50
Purchase #4	$18.49	6.567%	$19.7042	$19.70	$19.70	$19.70
Purchase #5	$44.83	9.682%	$49.1704	$49.17	$49.15	$49.20
Purchase #6	$93.57	10.149%	$103.0664	$103.07	$103.05	$103.10
Purchase #7	$219.72	12.535%	$247.2619	$247.26	$247.25	$247.30
7 purchase totals =	$897.26		$1,003.5273	$1,003.52	$1,003.50	$1,003.60