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	$87.48	13.600%	$99.3773	$99.38	$99.40	$99.40
Purchase #2	$171.45	5.294%	$180.5266	$180.53	$180.55	$180.50
Purchase #3	$122.82	8.156%	$132.8372	$132.84	$132.85	$132.80
Purchase #4	$27.45	3.662%	$28.4552	$28.46	$28.45	$28.50
Purchase #5	$5.51	10.533%	$6.0904	$6.09	$6.10	$6.10
Purchase #6	$68.85	3.250%	$71.0876	$71.09	$71.10	$71.10
Purchase #7	$32.69	6.873%	$34.9368	$34.94	$34.95	$34.90
7 purchase totals =	$516.25		$553.3111	$553.33	$553.40	$553.30