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	$129.39	13.787%	$147.229	$147.23	$147.25	$147.20
Purchase #2	$161.50	4.340%	$168.5091	$168.51	$168.50	$168.50
Purchase #3	$126.79	9.559%	$138.9099	$138.91	$138.90	$138.90
Purchase #4	$122.46	7.168%	$131.2379	$131.24	$131.25	$131.20
Purchase #5	$197.84	10.664%	$218.9377	$218.94	$218.95	$218.90
Purchase #6	$77.45	7.813%	$83.5012	$83.50	$83.50	$83.50
Purchase #7	$242.57	8.134%	$262.3006	$262.30	$262.30	$262.30
7 purchase totals =	$1,058.00		$1,150.6254	$1,150.63	$1,150.65	$1,150.50