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	$140.57	4.534%	$146.9434	$146.94	$146.95	$146.90
Purchase #2	$168.74	9.130%	$184.146	$184.15	$184.15	$184.10
Purchase #3	$236.86	12.856%	$267.3107	$267.31	$267.30	$267.30
Purchase #4	$83.80	7.673%	$90.23	$90.23	$90.25	$90.20
Purchase #5	$119.43	6.205%	$126.8406	$126.84	$126.85	$126.80
Purchase #6	$20.34	7.803%	$21.9271	$21.93	$21.95	$21.90
Purchase #7	$84.28	6.693%	$89.9209	$89.92	$89.90	$89.90
7 purchase totals =	$854.02		$927.3187	$927.32	$927.35	$927.10