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	$222.92	4.845%	$233.7205	$233.72	$233.70	$233.70
Purchase #2	$175.62	12.139%	$196.9385	$196.94	$196.95	$196.90
Purchase #3	$82.77	12.511%	$93.1254	$93.13	$93.15	$93.10
Purchase #4	$24.82	9.291%	$27.126	$27.13	$27.15	$27.10
Purchase #5	$196.38	12.761%	$221.4401	$221.44	$221.45	$221.40
Purchase #6	$17.30	4.124%	$18.0135	$18.01	$18.00	$18.00
Purchase #7	$83.61	5.223%	$87.977	$87.98	$88.00	$88.00
7 purchase totals =	$803.42		$878.3410	$878.35	$878.40	$878.20