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	$109.89	12.497%	$123.623	$123.62	$123.60	$123.60
Purchase #2	$197.98	4.194%	$206.2833	$206.28	$206.30	$206.30
Purchase #3	$40.80	9.832%	$44.8115	$44.81	$44.80	$44.80
Purchase #4	$7.31	8.441%	$7.927	$7.93	$7.95	$7.90
Purchase #5	$67.93	6.631%	$72.4344	$72.43	$72.45	$72.40
Purchase #6	$138.96	8.263%	$150.4423	$150.44	$150.45	$150.40
Purchase #7	$233.40	13.208%	$264.2275	$264.23	$264.25	$264.20
7 purchase totals =	$796.27		$869.7490	$869.74	$869.80	$869.60