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	$166.73	11.377%	$185.6989	$185.70	$185.70	$185.70
Purchase #2	$101.68	4.673%	$106.4315	$106.43	$106.45	$106.40
Purchase #3	$220.90	11.750%	$246.8558	$246.86	$246.85	$246.90
Purchase #4	$159.81	11.667%	$178.455	$178.46	$178.45	$178.50
Purchase #5	$101.63	4.241%	$105.9401	$105.94	$105.95	$105.90
Purchase #6	$73.67	12.764%	$83.0732	$83.07	$83.05	$83.10
Purchase #7	$37.49	13.442%	$42.5294	$42.53	$42.55	$42.50
7 purchase totals =	$861.91		$948.9839	$948.99	$949.00	$949.00