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	$147.76	3.133%	$152.3893	$152.39	$152.40	$152.40
Purchase #2	$69.94	12.814%	$78.9021	$78.90	$78.90	$78.90
Purchase #3	$228.50	3.111%	$235.6086	$235.61	$235.60	$235.60
Purchase #4	$247.97	8.667%	$269.4616	$269.46	$269.45	$269.50
Purchase #5	$73.32	5.719%	$77.5132	$77.51	$77.50	$77.50
Purchase #6	$93.49	7.400%	$100.4083	$100.41	$100.40	$100.40
Purchase #7	$29.34	8.572%	$31.855	$31.86	$31.85	$31.90
7 purchase totals =	$890.32		$946.1381	$946.14	$946.10	$946.20