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	$89.38	11.864%	$99.984	$99.98	$100.00	$100.00
Purchase #2	$230.75	7.842%	$248.8454	$248.85	$248.85	$248.80
Purchase #3	$175.95	5.506%	$185.6378	$185.64	$185.65	$185.60
Purchase #4	$31.91	5.546%	$33.6797	$33.68	$33.70	$33.70
Purchase #5	$147.61	3.560%	$152.8649	$152.86	$152.85	$152.90
Purchase #6	$85.95	5.679%	$90.8311	$90.83	$90.85	$90.80
Purchase #7	$128.34	6.557%	$136.7553	$136.76	$136.75	$136.80
7 purchase totals =	$889.89		$948.5982	$948.60	$948.65	$948.60