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	$29.59	13.296%	$33.5243	$33.52	$33.50	$33.50
Purchase #2	$48.89	13.272%	$55.3787	$55.38	$55.40	$55.40
Purchase #3	$230.47	10.483%	$254.6302	$254.63	$254.65	$254.60
Purchase #4	$96.74	7.254%	$103.7575	$103.76	$103.75	$103.80
Purchase #5	$160.44	6.513%	$170.8895	$170.89	$170.90	$170.90
Purchase #6	$183.34	3.568%	$189.8816	$189.88	$189.90	$189.90
Purchase #7	$61.67	9.197%	$67.3418	$67.34	$67.35	$67.30
7 purchase totals =	$811.14		$875.4036	$875.40	$875.45	$875.40