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	$133.46	7.791%	$143.8579	$143.86	$143.85	$143.90
Purchase #2	$178.82	6.873%	$191.1103	$191.11	$191.10	$191.10
Purchase #3	$121.81	8.163%	$131.7534	$131.75	$131.75	$131.80
Purchase #4	$73.73	9.180%	$80.4984	$80.50	$80.50	$80.50
Purchase #5	$14.69	3.282%	$15.1721	$15.17	$15.15	$15.20
Purchase #6	$149.38	13.680%	$169.8152	$169.82	$169.80	$169.80
Purchase #7	$78.80	8.156%	$85.2269	$85.23	$85.25	$85.20
7 purchase totals =	$750.69		$817.4342	$817.44	$817.40	$817.50