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	$37.48	5.483%	$39.535	$39.54	$39.55	$39.50
Purchase #2	$112.91	10.610%	$124.8898	$124.89	$124.90	$124.90
Purchase #3	$162.80	3.755%	$168.9131	$168.91	$168.90	$168.90
Purchase #4	$84.71	12.326%	$95.1514	$95.15	$95.15	$95.20
Purchase #5	$82.53	6.798%	$88.1404	$88.14	$88.15	$88.10
Purchase #6	$25.58	9.209%	$27.9357	$27.94	$27.95	$27.90
Purchase #7	$64.53	11.644%	$72.0439	$72.04	$72.05	$72.00
7 purchase totals =	$570.54		$616.6093	$616.61	$616.65	$616.50