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	$20.76	3.687%	$21.5254	$21.53	$21.55	$21.50
Purchase #2	$78.25	5.263%	$82.3683	$82.37	$82.35	$82.40
Purchase #3	$245.74	11.708%	$274.5112	$274.51	$274.50	$274.50
Purchase #4	$200.96	8.176%	$217.3905	$217.39	$217.40	$217.40
Purchase #5	$93.41	3.352%	$96.5411	$96.54	$96.55	$96.50
Purchase #6	$156.38	7.817%	$168.6042	$168.60	$168.60	$168.60
Purchase #7	$45.91	11.381%	$51.135	$51.14	$51.15	$51.10
7 purchase totals =	$841.41		$912.0757	$912.08	$912.10	$912.00