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	$113.38	11.709%	$126.6557	$126.66	$126.65	$126.70
Purchase #2	$224.50	9.506%	$245.841	$245.84	$245.85	$245.80
Purchase #3	$242.42	6.628%	$258.4876	$258.49	$258.50	$258.50
Purchase #4	$93.57	13.391%	$106.1	$106.10	$106.10	$106.10
Purchase #5	$215.97	12.746%	$243.4975	$243.50	$243.50	$243.50
Purchase #6	$54.96	8.394%	$59.5733	$59.57	$59.55	$59.60
Purchase #7	$79.75	13.164%	$90.2483	$90.25	$90.25	$90.20
7 purchase totals =	$1,024.55		$1,130.4034	$1,130.41	$1,130.40	$1,130.40