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	$246.39	9.645%	$270.1543	$270.15	$270.15	$270.20
Purchase #2	$170.67	8.604%	$185.3544	$185.35	$185.35	$185.40
Purchase #3	$94.37	5.229%	$99.3046	$99.30	$99.30	$99.30
Purchase #4	$116.59	7.697%	$125.5639	$125.56	$125.55	$125.60
Purchase #5	$68.92	4.698%	$72.1579	$72.16	$72.15	$72.20
Purchase #6	$52.95	5.683%	$55.9591	$55.96	$55.95	$56.00
Purchase #7	$16.80	4.525%	$17.5602	$17.56	$17.55	$17.60
7 purchase totals =	$766.69		$826.0544	$826.04	$826.00	$826.30