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	$246.32	8.115%	$266.3089	$266.31	$266.30	$266.30
Purchase #2	$40.76	4.217%	$42.4788	$42.48	$42.50	$42.50
Purchase #3	$95.64	11.493%	$106.6319	$106.63	$106.65	$106.60
Purchase #4	$63.25	6.463%	$67.3378	$67.34	$67.35	$67.30
Purchase #5	$65.35	10.556%	$72.2483	$72.25	$72.25	$72.20
Purchase #6	$218.94	8.542%	$237.6419	$237.64	$237.65	$237.60
Purchase #7	$196.33	5.552%	$207.2302	$207.23	$207.25	$207.20
7 purchase totals =	$926.59		$999.8778	$999.88	$999.95	$999.70