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	$227.77	13.498%	$258.5144	$258.51	$258.50	$258.50
Purchase #2	$136.36	7.148%	$146.107	$146.11	$146.10	$146.10
Purchase #3	$164.43	6.146%	$174.5359	$174.54	$174.55	$174.50
Purchase #4	$234.59	8.210%	$253.8498	$253.85	$253.85	$253.80
Purchase #5	$32.79	13.528%	$37.2258	$37.23	$37.25	$37.20
Purchase #6	$62.50	4.643%	$65.4019	$65.40	$65.40	$65.40
Purchase #7	$16.39	13.265%	$18.5641	$18.56	$18.55	$18.60
7 purchase totals =	$874.83		$954.1989	$954.20	$954.20	$954.10