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	$14.26	7.537%	$15.3348	$15.33	$15.35	$15.30
Purchase #2	$215.53	12.714%	$242.9325	$242.93	$242.95	$242.90
Purchase #3	$166.98	7.224%	$179.0426	$179.04	$179.05	$179.00
Purchase #4	$164.69	10.676%	$182.2723	$182.27	$182.25	$182.30
Purchase #5	$83.72	6.718%	$89.3443	$89.34	$89.35	$89.30
Purchase #6	$57.37	7.419%	$61.6263	$61.63	$61.65	$61.60
Purchase #7	$11.39	7.153%	$12.2047	$12.20	$12.20	$12.20
7 purchase totals =	$713.94		$782.7575	$782.74	$782.80	$782.60