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	$77.59	6.392%	$82.5496	$82.55	$82.55	$82.50
Purchase #2	$108.44	11.226%	$120.6135	$120.61	$120.60	$120.60
Purchase #3	$175.26	9.668%	$192.2041	$192.20	$192.20	$192.20
Purchase #4	$81.38	11.259%	$90.5426	$90.54	$90.55	$90.50
Purchase #5	$117.83	11.356%	$131.2108	$131.21	$131.20	$131.20
Purchase #6	$43.72	8.578%	$47.4703	$47.47	$47.45	$47.50
Purchase #7	$162.92	4.584%	$170.3883	$170.39	$170.40	$170.40
7 purchase totals =	$767.14		$834.9792	$834.97	$834.95	$834.90