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	$11.89	8.682%	$12.9223	$12.92	$12.90	$12.90
Purchase #2	$185.33	8.217%	$200.5586	$200.56	$200.55	$200.60
Purchase #3	$97.90	7.707%	$105.4452	$105.45	$105.45	$105.40
Purchase #4	$115.61	8.632%	$125.5895	$125.59	$125.60	$125.60
Purchase #5	$166.89	7.257%	$179.0012	$179.00	$179.00	$179.00
Purchase #6	$92.36	8.748%	$100.4397	$100.44	$100.45	$100.40
Purchase #7	$23.61	8.316%	$25.5734	$25.57	$25.55	$25.60
7 purchase totals =	$693.59		$749.5299	$749.53	$749.50	$749.50