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	$24.34	8.463%	$26.3999	$26.40	$26.40	$26.40
Purchase #2	$77.82	13.275%	$88.1506	$88.15	$88.15	$88.20
Purchase #3	$57.30	4.580%	$59.9243	$59.92	$59.90	$59.90
Purchase #4	$218.74	12.676%	$246.4675	$246.47	$246.45	$246.50
Purchase #5	$82.59	9.871%	$90.7425	$90.74	$90.75	$90.70
Purchase #6	$150.65	10.503%	$166.4728	$166.47	$166.45	$166.50
Purchase #7	$125.88	9.412%	$137.7278	$137.73	$137.75	$137.70
7 purchase totals =	$737.32		$815.8854	$815.88	$815.85	$815.90