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	$31.64	10.280%	$34.8926	$34.89	$34.90	$34.90
Purchase #2	$207.78	4.197%	$216.5005	$216.50	$216.50	$216.50
Purchase #3	$74.61	10.448%	$82.4053	$82.41	$82.40	$82.40
Purchase #4	$178.47	13.769%	$203.0435	$203.04	$203.05	$203.00
Purchase #5	$170.37	6.394%	$181.2635	$181.26	$181.25	$181.30
Purchase #6	$236.60	3.438%	$244.7343	$244.73	$244.75	$244.70
Purchase #7	$124.43	10.320%	$137.2712	$137.27	$137.25	$137.30
7 purchase totals =	$1,023.90		$1,100.1109	$1,100.10	$1,100.10	$1,100.10