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	$75.36	3.164%	$77.7444	$77.74	$77.75	$77.70
Purchase #2	$147.28	11.649%	$164.4366	$164.44	$164.45	$164.40
Purchase #3	$44.51	10.569%	$49.2143	$49.21	$49.20	$49.20
Purchase #4	$52.54	4.398%	$54.8507	$54.85	$54.85	$54.90
Purchase #5	$128.86	9.680%	$141.3336	$141.33	$141.35	$141.30
Purchase #6	$24.38	10.281%	$26.8865	$26.89	$26.90	$26.90
Purchase #7	$83.80	7.706%	$90.2576	$90.26	$90.25	$90.30
7 purchase totals =	$556.73		$604.7237	$604.72	$604.75	$604.70