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	$32.96	13.774%	$37.4999	$37.50	$37.50	$37.50
Purchase #2	$208.96	12.374%	$234.8167	$234.82	$234.80	$234.80
Purchase #3	$135.86	3.317%	$140.3665	$140.37	$140.35	$140.40
Purchase #4	$113.25	13.117%	$128.105	$128.11	$128.10	$128.10
Purchase #5	$223.62	6.110%	$237.2832	$237.28	$237.30	$237.30
Purchase #6	$181.38	3.439%	$187.6177	$187.62	$187.60	$187.60
Purchase #7	$204.56	9.185%	$223.3488	$223.35	$223.35	$223.30
7 purchase totals =	$1,100.59		$1,189.0378	$1,189.05	$1,189.00	$1,189.00