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	$102.96	8.601%	$111.8156	$111.82	$111.80	$111.80
Purchase #2	$56.44	9.685%	$61.9062	$61.91	$61.90	$61.90
Purchase #3	$116.54	5.740%	$123.2294	$123.23	$123.25	$123.20
Purchase #4	$13.90	9.626%	$15.238	$15.24	$15.25	$15.20
Purchase #5	$243.57	8.574%	$264.4537	$264.45	$264.45	$264.50
Purchase #6	$25.56	7.501%	$27.4773	$27.48	$27.50	$27.50
Purchase #7	$222.26	10.470%	$245.5306	$245.53	$245.55	$245.50
7 purchase totals =	$781.23		$849.6508	$849.66	$849.70	$849.60