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	$38.88	8.760%	$42.2859	$42.29	$42.30	$42.30
Purchase #2	$144.58	12.672%	$162.9012	$162.90	$162.90	$162.90
Purchase #3	$166.79	8.298%	$180.6302	$180.63	$180.65	$180.60
Purchase #4	$247.80	11.433%	$276.131	$276.13	$276.15	$276.10
Purchase #5	$17.74	13.650%	$20.1615	$20.16	$20.15	$20.20
Purchase #6	$188.38	5.556%	$198.8464	$198.85	$198.85	$198.80
Purchase #7	$170.37	3.477%	$176.2938	$176.29	$176.30	$176.30
7 purchase totals =	$974.54		$1,057.2500	$1,057.25	$1,057.30	$1,057.20