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	$123.65	13.534%	$140.3848	$140.38	$140.40	$140.40
Purchase #2	$134.39	4.608%	$140.5827	$140.58	$140.60	$140.60
Purchase #3	$25.85	11.588%	$28.8455	$28.85	$28.85	$28.80
Purchase #4	$38.79	4.451%	$40.5165	$40.52	$40.50	$40.50
Purchase #5	$193.33	3.807%	$200.6901	$200.69	$200.70	$200.70
Purchase #6	$116.59	11.686%	$130.2147	$130.21	$130.20	$130.20
Purchase #7	$77.81	12.213%	$87.3129	$87.31	$87.30	$87.30
7 purchase totals =	$710.41		$768.5472	$768.54	$768.55	$768.50