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	$83.65	3.318%	$86.4255	$86.43	$86.45	$86.40
Purchase #2	$109.52	12.797%	$123.5353	$123.54	$123.55	$123.50
Purchase #3	$170.93	10.458%	$188.8059	$188.81	$188.80	$188.80
Purchase #4	$120.43	8.820%	$131.0519	$131.05	$131.05	$131.10
Purchase #5	$127.62	6.160%	$135.4814	$135.48	$135.50	$135.50
Purchase #6	$220.92	12.328%	$248.155	$248.16	$248.15	$248.20
Purchase #7	$203.83	11.570%	$227.4131	$227.41	$227.40	$227.40
7 purchase totals =	$1,036.90		$1,140.8681	$1,140.88	$1,140.90	$1,140.90