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	$91.34	8.797%	$99.3752	$99.38	$99.40	$99.40
Purchase #2	$68.87	13.835%	$78.3982	$78.40	$78.40	$78.40
Purchase #3	$63.46	11.730%	$70.9039	$70.90	$70.90	$70.90
Purchase #4	$154.41	5.329%	$162.6385	$162.64	$162.65	$162.60
Purchase #5	$28.73	6.175%	$30.5041	$30.50	$30.50	$30.50
Purchase #6	$79.34	5.741%	$83.8949	$83.89	$83.90	$83.90
Purchase #7	$82.62	5.185%	$86.9038	$86.90	$86.90	$86.90
7 purchase totals =	$568.77		$612.6186	$612.61	$612.65	$612.60