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	$125.95	4.317%	$131.3873	$131.39	$131.40	$131.40
Purchase #2	$55.41	13.297%	$62.7779	$62.78	$62.80	$62.80
Purchase #3	$107.34	12.627%	$120.8938	$120.89	$120.90	$120.90
Purchase #4	$137.78	10.410%	$152.1229	$152.12	$152.10	$152.10
Purchase #5	$221.79	8.339%	$240.2851	$240.29	$240.30	$240.30
Purchase #6	$13.84	11.626%	$15.449	$15.45	$15.45	$15.40
Purchase #7	$222.95	11.487%	$248.5603	$248.56	$248.55	$248.60
7 purchase totals =	$885.06		$971.4763	$971.48	$971.50	$971.50