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	$125.34	11.481%	$139.7303	$139.73	$139.75	$139.70
Purchase #2	$243.91	10.456%	$269.4132	$269.41	$269.40	$269.40
Purchase #3	$81.41	10.614%	$90.0509	$90.05	$90.05	$90.10
Purchase #4	$237.58	3.499%	$245.8929	$245.89	$245.90	$245.90
Purchase #5	$136.83	11.395%	$152.4218	$152.42	$152.40	$152.40
Purchase #6	$129.82	7.799%	$139.9447	$139.94	$139.95	$139.90
Purchase #7	$222.55	8.278%	$240.9727	$240.97	$240.95	$241.00
7 purchase totals =	$1,177.44		$1,278.4265	$1,278.41	$1,278.40	$1,278.40