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	$85.80	5.202%	$90.2633	$90.26	$90.25	$90.30
Purchase #2	$250.65	6.775%	$267.6315	$267.63	$267.65	$267.60
Purchase #3	$64.60	11.343%	$71.9276	$71.93	$71.95	$71.90
Purchase #4	$217.56	12.305%	$244.3308	$244.33	$244.35	$244.30
Purchase #5	$94.25	7.759%	$101.5629	$101.56	$101.55	$101.60
Purchase #6	$106.38	9.801%	$116.8063	$116.81	$116.80	$116.80
Purchase #7	$76.76	12.288%	$86.1923	$86.19	$86.20	$86.20
7 purchase totals =	$896.00		$978.7147	$978.71	$978.75	$978.70