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	$90.96	5.841%	$96.273	$96.27	$96.25	$96.30
Purchase #2	$100.50	4.427%	$104.9491	$104.95	$104.95	$104.90
Purchase #3	$135.33	5.284%	$142.4808	$142.48	$142.50	$142.50
Purchase #4	$207.98	8.367%	$225.3817	$225.38	$225.40	$225.40
Purchase #5	$35.86	13.864%	$40.8316	$40.83	$40.85	$40.80
Purchase #6	$102.30	3.506%	$105.8866	$105.89	$105.90	$105.90
Purchase #7	$148.52	4.275%	$154.8692	$154.87	$154.85	$154.90
7 purchase totals =	$821.45		$870.6720	$870.67	$870.70	$870.70