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	$83.83	9.281%	$91.6103	$91.61	$91.60	$91.60
Purchase #2	$107.34	13.555%	$121.8899	$121.89	$121.90	$121.90
Purchase #3	$75.38	4.185%	$78.5347	$78.53	$78.55	$78.50
Purchase #4	$183.53	4.438%	$191.6751	$191.68	$191.70	$191.70
Purchase #5	$18.53	10.626%	$20.499	$20.50	$20.50	$20.50
Purchase #6	$41.60	9.178%	$45.418	$45.42	$45.40	$45.40
Purchase #7	$246.63	9.616%	$270.3459	$270.35	$270.35	$270.30
7 purchase totals =	$756.84		$819.9729	$819.98	$820.00	$819.90