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	$83.75	8.112%	$90.5438	$90.54	$90.55	$90.50
Purchase #2	$249.71	3.686%	$258.9143	$258.91	$258.90	$258.90
Purchase #3	$72.68	13.561%	$82.5361	$82.54	$82.55	$82.50
Purchase #4	$100.67	4.330%	$105.029	$105.03	$105.05	$105.00
Purchase #5	$126.44	7.789%	$136.2884	$136.29	$136.30	$136.30
Purchase #6	$65.41	5.846%	$69.2339	$69.23	$69.25	$69.20
Purchase #7	$44.53	13.579%	$50.5767	$50.58	$50.60	$50.60
7 purchase totals =	$743.19		$793.1222	$793.12	$793.20	$793.00