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	$40.51	5.439%	$42.7133	$42.71	$42.70	$42.70
Purchase #2	$38.53	7.277%	$41.3338	$41.33	$41.35	$41.30
Purchase #3	$127.44	3.471%	$131.8634	$131.86	$131.85	$131.90
Purchase #4	$134.44	9.798%	$147.6124	$147.61	$147.60	$147.60
Purchase #5	$245.51	5.698%	$259.4992	$259.50	$259.50	$259.50
Purchase #6	$85.30	5.202%	$89.7373	$89.74	$89.75	$89.70
Purchase #7	$61.32	13.836%	$69.8042	$69.80	$69.80	$69.80
7 purchase totals =	$733.05		$782.5636	$782.55	$782.55	$782.50