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	$27.44	4.774%	$28.75	$28.75	$28.75	$28.80
Purchase #2	$92.30	10.345%	$101.8484	$101.85	$101.85	$101.80
Purchase #3	$24.50	5.419%	$25.8277	$25.83	$25.85	$25.80
Purchase #4	$246.42	11.331%	$274.3419	$274.34	$274.35	$274.30
Purchase #5	$132.79	6.248%	$141.0867	$141.09	$141.10	$141.10
Purchase #6	$48.84	3.519%	$50.5587	$50.56	$50.55	$50.60
Purchase #7	$182.87	7.245%	$196.1189	$196.12	$196.10	$196.10
7 purchase totals =	$755.16		$818.5323	$818.54	$818.55	$818.50