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	$93.46	6.194%	$99.2489	$99.25	$99.25	$99.20
Purchase #2	$18.98	10.126%	$20.9019	$20.90	$20.90	$20.90
Purchase #3	$92.78	11.415%	$103.3708	$103.37	$103.35	$103.40
Purchase #4	$137.35	6.141%	$145.7847	$145.78	$145.80	$145.80
Purchase #5	$194.47	13.359%	$220.4492	$220.45	$220.45	$220.40
Purchase #6	$67.41	6.832%	$72.0155	$72.02	$72.00	$72.00
Purchase #7	$181.30	7.432%	$194.7742	$194.77	$194.75	$194.80
7 purchase totals =	$785.75		$856.5452	$856.54	$856.50	$856.50