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	$24.97	8.423%	$27.0732	$27.07	$27.05	$27.10
Purchase #2	$166.65	4.410%	$173.9993	$174.00	$174.00	$174.00
Purchase #3	$83.71	5.731%	$88.5074	$88.51	$88.50	$88.50
Purchase #4	$67.86	6.569%	$72.3177	$72.32	$72.30	$72.30
Purchase #5	$39.59	7.241%	$42.4567	$42.46	$42.45	$42.50
Purchase #6	$106.37	10.282%	$117.307	$117.31	$117.30	$117.30
Purchase #7	$17.63	9.747%	$19.3484	$19.35	$19.35	$19.30
7 purchase totals =	$506.78		$541.0097	$541.02	$540.95	$541.00