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	$52.54	13.263%	$59.5084	$59.51	$59.50	$59.50
Purchase #2	$63.49	5.589%	$67.0385	$67.04	$67.05	$67.00
Purchase #3	$151.69	9.786%	$166.5344	$166.53	$166.55	$166.50
Purchase #4	$73.68	11.303%	$82.0081	$82.01	$82.00	$82.00
Purchase #5	$97.96	6.378%	$104.2079	$104.21	$104.20	$104.20
Purchase #6	$36.98	9.126%	$40.3548	$40.35	$40.35	$40.40
Purchase #7	$160.55	13.610%	$182.4009	$182.40	$182.40	$182.40
7 purchase totals =	$636.89		$702.0530	$702.05	$702.05	$702.00