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	$137.26	13.590%	$155.9136	$155.91	$155.90	$155.90
Purchase #2	$192.43	7.273%	$206.4254	$206.43	$206.45	$206.40
Purchase #3	$247.46	6.815%	$264.3244	$264.32	$264.30	$264.30
Purchase #4	$33.81	10.593%	$37.3915	$37.39	$37.40	$37.40
Purchase #5	$31.39	5.159%	$33.0094	$33.01	$33.00	$33.00
Purchase #6	$46.56	9.224%	$50.8547	$50.85	$50.85	$50.90
Purchase #7	$161.75	10.745%	$179.13	$179.13	$179.15	$179.10
7 purchase totals =	$850.66		$927.0490	$927.04	$927.05	$927.00