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	$14.78	4.862%	$15.4986	$15.50	$15.50	$15.50
Purchase #2	$34.55	5.148%	$36.3286	$36.33	$36.35	$36.30
Purchase #3	$45.52	10.669%	$50.3765	$50.38	$50.40	$50.40
Purchase #4	$197.73	6.431%	$210.446	$210.45	$210.45	$210.40
Purchase #5	$198.47	12.806%	$223.8861	$223.89	$223.90	$223.90
Purchase #6	$67.92	8.659%	$73.8012	$73.80	$73.80	$73.80
Purchase #7	$44.57	13.317%	$50.5054	$50.51	$50.50	$50.50
7 purchase totals =	$603.54		$660.8424	$660.86	$660.90	$660.80