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	$128.43	12.393%	$144.3463	$144.35	$144.35	$144.30
Purchase #2	$166.82	7.227%	$178.8761	$178.88	$178.90	$178.90
Purchase #3	$123.51	13.264%	$139.8924	$139.89	$139.90	$139.90
Purchase #4	$59.51	10.805%	$65.9401	$65.94	$65.95	$65.90
Purchase #5	$40.86	11.524%	$45.5687	$45.57	$45.55	$45.60
Purchase #6	$133.90	10.176%	$147.5257	$147.53	$147.55	$147.50
Purchase #7	$57.34	3.520%	$59.3584	$59.36	$59.35	$59.40
7 purchase totals =	$710.37		$781.5077	$781.52	$781.55	$781.50