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	$147.56	3.812%	$153.185	$153.19	$153.20	$153.20
Purchase #2	$123.42	13.402%	$139.9607	$139.96	$139.95	$140.00
Purchase #3	$50.56	8.654%	$54.9355	$54.94	$54.95	$54.90
Purchase #4	$22.59	13.864%	$25.7219	$25.72	$25.70	$25.70
Purchase #5	$192.32	3.642%	$199.3243	$199.32	$199.30	$199.30
Purchase #6	$109.60	4.567%	$114.6054	$114.61	$114.60	$114.60
Purchase #7	$205.56	11.590%	$229.3844	$229.38	$229.40	$229.40
7 purchase totals =	$851.61		$917.1172	$917.12	$917.10	$917.10