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	$137.66	6.637%	$146.7965	$146.80	$146.80	$146.80
Purchase #2	$12.82	4.702%	$13.4228	$13.42	$13.40	$13.40
Purchase #3	$158.84	12.797%	$179.1668	$179.17	$179.15	$179.20
Purchase #4	$202.97	8.574%	$220.3726	$220.37	$220.35	$220.40
Purchase #5	$56.58	10.112%	$62.3014	$62.30	$62.30	$62.30
Purchase #6	$31.63	13.443%	$35.882	$35.88	$35.90	$35.90
Purchase #7	$197.81	12.500%	$222.5363	$222.54	$222.55	$222.50
7 purchase totals =	$798.31		$880.4784	$880.48	$880.45	$880.50