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	$38.28	10.441%	$42.2768	$42.28	$42.30	$42.30
Purchase #2	$221.46	13.298%	$250.9098	$250.91	$250.90	$250.90
Purchase #3	$50.76	11.390%	$56.5416	$56.54	$56.55	$56.50
Purchase #4	$83.97	12.871%	$94.7778	$94.78	$94.80	$94.80
Purchase #5	$36.38	5.261%	$38.294	$38.29	$38.30	$38.30
Purchase #6	$15.45	13.657%	$17.56	$17.56	$17.55	$17.60
Purchase #7	$248.90	6.306%	$264.5956	$264.60	$264.60	$264.60
7 purchase totals =	$695.20		$764.9556	$764.96	$765.00	$765.00