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	$51.61	13.306%	$58.4772	$58.48	$58.50	$58.50
Purchase #2	$159.44	5.511%	$168.2267	$168.23	$168.25	$168.20
Purchase #3	$143.36	6.442%	$152.5953	$152.60	$152.60	$152.60
Purchase #4	$118.86	4.239%	$123.8985	$123.90	$123.90	$123.90
Purchase #5	$102.73	6.558%	$109.467	$109.47	$109.45	$109.50
Purchase #6	$74.47	4.196%	$77.5948	$77.59	$77.60	$77.60
Purchase #7	$120.61	12.569%	$135.7695	$135.77	$135.75	$135.80
7 purchase totals =	$771.08		$826.0290	$826.04	$826.05	$826.10