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	$37.61	12.760%	$42.409	$42.41	$42.40	$42.40
Purchase #2	$64.38	10.642%	$71.2313	$71.23	$71.25	$71.20
Purchase #3	$209.43	5.603%	$221.1644	$221.16	$221.15	$221.20
Purchase #4	$38.94	12.762%	$43.9095	$43.91	$43.90	$43.90
Purchase #5	$50.29	10.241%	$55.4402	$55.44	$55.45	$55.40
Purchase #6	$223.58	5.418%	$235.6936	$235.69	$235.70	$235.70
Purchase #7	$37.75	11.707%	$42.1694	$42.17	$42.15	$42.20
7 purchase totals =	$661.98		$712.0174	$712.01	$712.00	$712.00