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	$98.63	10.398%	$108.8855	$108.89	$108.90	$108.90
Purchase #2	$183.46	13.188%	$207.6547	$207.65	$207.65	$207.70
Purchase #3	$79.48	5.611%	$83.9396	$83.94	$83.95	$83.90
Purchase #4	$80.98	12.225%	$90.8798	$90.88	$90.90	$90.90
Purchase #5	$78.67	5.297%	$82.8371	$82.84	$82.85	$82.80
Purchase #6	$60.75	11.740%	$67.8821	$67.88	$67.90	$67.90
Purchase #7	$41.73	4.492%	$43.6045	$43.60	$43.60	$43.60
7 purchase totals =	$623.70		$685.6833	$685.68	$685.75	$685.70