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	$10.59	12.804%	$11.9459	$11.95	$11.95	$11.90
Purchase #2	$81.90	5.256%	$86.2047	$86.20	$86.20	$86.20
Purchase #3	$115.71	4.434%	$120.8406	$120.84	$120.85	$120.80
Purchase #4	$243.66	13.787%	$277.2534	$277.25	$277.25	$277.30
Purchase #5	$212.66	5.293%	$223.9161	$223.92	$223.90	$223.90
Purchase #6	$200.37	10.735%	$221.8797	$221.88	$221.90	$221.90
Purchase #7	$55.57	10.867%	$61.6088	$61.61	$61.60	$61.60
7 purchase totals =	$920.46		$1,003.6492	$1,003.65	$1,003.65	$1,003.60