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	$19.32	13.387%	$21.9064	$21.91	$21.90	$21.90
Purchase #2	$51.78	9.174%	$56.5303	$56.53	$56.55	$56.50
Purchase #3	$82.52	9.614%	$90.4535	$90.45	$90.45	$90.50
Purchase #4	$15.27	7.223%	$16.373	$16.37	$16.35	$16.40
Purchase #5	$206.61	7.680%	$222.4776	$222.48	$222.50	$222.50
Purchase #6	$173.54	10.774%	$192.2372	$192.24	$192.25	$192.20
Purchase #7	$63.41	12.709%	$71.4688	$71.47	$71.45	$71.50
7 purchase totals =	$612.45		$671.4468	$671.45	$671.45	$671.50