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	$51.53	11.431%	$57.4204	$57.42	$57.40	$57.40
Purchase #2	$86.37	5.688%	$91.2827	$91.28	$91.30	$91.30
Purchase #3	$195.46	12.281%	$219.4644	$219.46	$219.45	$219.50
Purchase #4	$240.84	13.569%	$273.5196	$273.52	$273.50	$273.50
Purchase #5	$164.30	13.139%	$185.8874	$185.89	$185.90	$185.90
Purchase #6	$6.25	9.428%	$6.8393	$6.84	$6.85	$6.80
Purchase #7	$171.65	7.161%	$183.9419	$183.94	$183.95	$183.90
7 purchase totals =	$916.40		$1,018.3557	$1,018.35	$1,018.35	$1,018.30