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	$93.46	7.351%	$100.3302	$100.33	$100.35	$100.30
Purchase #2	$137.90	6.491%	$146.8511	$146.85	$146.85	$146.90
Purchase #3	$33.98	4.317%	$35.4469	$35.45	$35.45	$35.40
Purchase #4	$116.68	6.713%	$124.5127	$124.51	$124.50	$124.50
Purchase #5	$11.50	10.660%	$12.7259	$12.73	$12.75	$12.70
Purchase #6	$86.54	12.747%	$97.5713	$97.57	$97.55	$97.60
Purchase #7	$101.49	10.689%	$112.3383	$112.34	$112.35	$112.30
7 purchase totals =	$581.55		$629.7764	$629.78	$629.80	$629.70