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	$85.25	7.772%	$91.8756	$91.88	$91.90	$91.90
Purchase #2	$238.45	3.792%	$247.492	$247.49	$247.50	$247.50
Purchase #3	$30.35	11.140%	$33.731	$33.73	$33.75	$33.70
Purchase #4	$105.27	10.749%	$116.5855	$116.59	$116.60	$116.60
Purchase #5	$84.54	6.646%	$90.1585	$90.16	$90.15	$90.20
Purchase #6	$15.88	3.210%	$16.3897	$16.39	$16.40	$16.40
Purchase #7	$133.44	10.166%	$147.0055	$147.01	$147.00	$147.00
7 purchase totals =	$693.18		$743.2378	$743.25	$743.30	$743.30