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	$173.36	6.317%	$184.3112	$184.31	$184.30	$184.30
Purchase #2	$90.39	3.400%	$93.4633	$93.46	$93.45	$93.50
Purchase #3	$224.32	11.691%	$250.5453	$250.55	$250.55	$250.50
Purchase #4	$136.59	11.443%	$152.22	$152.22	$152.20	$152.20
Purchase #5	$76.61	10.563%	$84.7023	$84.70	$84.70	$84.70
Purchase #6	$168.75	9.540%	$184.8488	$184.85	$184.85	$184.80
Purchase #7	$242.96	12.290%	$272.8198	$272.82	$272.80	$272.80
7 purchase totals =	$1,112.98		$1,222.9107	$1,222.91	$1,222.85	$1,222.80