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	$109.50	12.492%	$123.1787	$123.18	$123.20	$123.20
Purchase #2	$31.44	3.750%	$32.619	$32.62	$32.60	$32.60
Purchase #3	$37.69	12.466%	$42.3884	$42.39	$42.40	$42.40
Purchase #4	$72.34	12.226%	$81.1843	$81.18	$81.20	$81.20
Purchase #5	$37.33	11.264%	$41.5349	$41.53	$41.55	$41.50
Purchase #6	$63.93	12.206%	$71.7333	$71.73	$71.75	$71.70
Purchase #7	$157.75	6.354%	$167.7734	$167.77	$167.75	$167.80
7 purchase totals =	$509.98		$560.4120	$560.40	$560.45	$560.40