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	$152.59	11.206%	$169.6892	$169.69	$169.70	$169.70
Purchase #2	$135.56	3.506%	$140.3127	$140.31	$140.30	$140.30
Purchase #3	$22.65	8.668%	$24.6133	$24.61	$24.60	$24.60
Purchase #4	$55.42	6.820%	$59.1996	$59.20	$59.20	$59.20
Purchase #5	$138.88	12.561%	$156.3247	$156.32	$156.30	$156.30
Purchase #6	$23.79	4.521%	$24.8655	$24.87	$24.85	$24.90
Purchase #7	$96.96	13.378%	$109.9313	$109.93	$109.95	$109.90
7 purchase totals =	$625.85		$684.9363	$684.93	$684.90	$684.90