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	$18.90	6.416%	$20.1126	$20.11	$20.10	$20.10
Purchase #2	$192.89	8.548%	$209.3782	$209.38	$209.40	$209.40
Purchase #3	$209.48	6.236%	$222.5432	$222.54	$222.55	$222.50
Purchase #4	$64.48	9.743%	$70.7623	$70.76	$70.75	$70.80
Purchase #5	$37.80	12.106%	$42.3761	$42.38	$42.40	$42.40
Purchase #6	$195.83	6.165%	$207.9029	$207.90	$207.90	$207.90
Purchase #7	$249.38	13.674%	$283.4802	$283.48	$283.50	$283.50
7 purchase totals =	$968.76		$1,056.5555	$1,056.55	$1,056.60	$1,056.60