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	$31.28	8.429%	$33.9166	$33.92	$33.90	$33.90
Purchase #2	$200.57	7.332%	$215.2758	$215.28	$215.30	$215.30
Purchase #3	$131.80	4.599%	$137.8615	$137.86	$137.85	$137.90
Purchase #4	$181.91	5.498%	$191.9114	$191.91	$191.90	$191.90
Purchase #5	$185.89	3.230%	$191.8942	$191.89	$191.90	$191.90
Purchase #6	$40.48	12.851%	$45.6821	$45.68	$45.70	$45.70
Purchase #7	$164.74	6.686%	$175.7545	$175.75	$175.75	$175.80
7 purchase totals =	$936.67		$992.2961	$992.29	$992.30	$992.40