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	$219.53	12.233%	$246.3851	$246.39	$246.40	$246.40
Purchase #2	$123.68	12.741%	$139.4381	$139.44	$139.45	$139.40
Purchase #3	$50.31	7.452%	$54.0591	$54.06	$54.05	$54.10
Purchase #4	$19.89	7.233%	$21.3286	$21.33	$21.35	$21.30
Purchase #5	$72.85	6.479%	$77.57	$77.57	$77.55	$77.60
Purchase #6	$216.39	7.841%	$233.3571	$233.36	$233.35	$233.40
Purchase #7	$195.86	8.386%	$212.2848	$212.28	$212.30	$212.30
7 purchase totals =	$898.51		$984.4228	$984.43	$984.45	$984.50