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	$51.25	8.798%	$55.759	$55.76	$55.75	$55.80
Purchase #2	$218.84	7.298%	$234.8109	$234.81	$234.80	$234.80
Purchase #3	$145.55	3.675%	$150.899	$150.90	$150.90	$150.90
Purchase #4	$55.40	12.559%	$62.3577	$62.36	$62.35	$62.40
Purchase #5	$160.79	6.182%	$170.73	$170.73	$170.75	$170.70
Purchase #6	$247.34	11.338%	$275.3834	$275.38	$275.40	$275.40
Purchase #7	$152.31	10.587%	$168.4351	$168.44	$168.45	$168.40
7 purchase totals =	$1,031.48		$1,118.3751	$1,118.38	$1,118.40	$1,118.40