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	$129.51	6.613%	$138.0745	$138.07	$138.05	$138.10
Purchase #2	$53.59	11.347%	$59.6709	$59.67	$59.65	$59.70
Purchase #3	$171.33	11.804%	$191.5538	$191.55	$191.55	$191.60
Purchase #4	$80.84	13.131%	$91.4551	$91.46	$91.45	$91.50
Purchase #5	$196.59	8.818%	$213.9253	$213.93	$213.95	$213.90
Purchase #6	$178.56	5.370%	$188.1487	$188.15	$188.15	$188.10
Purchase #7	$66.79	10.714%	$73.9459	$73.95	$73.95	$73.90
7 purchase totals =	$877.21		$956.7742	$956.78	$956.75	$956.80