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	$140.56	12.339%	$157.9037	$157.90	$157.90	$157.90
Purchase #2	$73.98	8.832%	$80.5139	$80.51	$80.50	$80.50
Purchase #3	$209.79	11.111%	$233.0998	$233.10	$233.10	$233.10
Purchase #4	$145.46	4.781%	$152.4144	$152.41	$152.40	$152.40
Purchase #5	$37.35	4.465%	$39.0177	$39.02	$39.00	$39.00
Purchase #6	$161.82	13.515%	$183.69	$183.69	$183.70	$183.70
Purchase #7	$75.31	4.191%	$78.4662	$78.47	$78.45	$78.50
7 purchase totals =	$844.27		$925.1057	$925.10	$925.05	$925.10