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	$56.78	5.510%	$59.9086	$59.91	$59.90	$59.90
Purchase #2	$139.51	9.757%	$153.122	$153.12	$153.10	$153.10
Purchase #3	$64.70	4.242%	$67.4446	$67.44	$67.45	$67.40
Purchase #4	$97.54	12.698%	$109.9256	$109.93	$109.95	$109.90
Purchase #5	$137.77	9.336%	$150.6322	$150.63	$150.65	$150.60
Purchase #6	$89.42	7.678%	$96.2857	$96.29	$96.30	$96.30
Purchase #7	$213.34	11.579%	$238.0426	$238.04	$238.05	$238.00
7 purchase totals =	$799.06		$875.3613	$875.36	$875.40	$875.20