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	$126.74	6.823%	$135.3875	$135.39	$135.40	$135.40
Purchase #2	$250.56	12.736%	$282.4713	$282.47	$282.45	$282.50
Purchase #3	$172.78	10.742%	$191.34	$191.34	$191.35	$191.30
Purchase #4	$131.98	7.700%	$142.1425	$142.14	$142.15	$142.10
Purchase #5	$230.61	10.648%	$255.1654	$255.17	$255.15	$255.20
Purchase #6	$227.34	4.873%	$238.4183	$238.42	$238.40	$238.40
Purchase #7	$43.82	8.202%	$47.4141	$47.41	$47.40	$47.40
7 purchase totals =	$1,183.83		$1,292.3391	$1,292.34	$1,292.30	$1,292.30