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	$11.94	5.550%	$12.6027	$12.60	$12.60	$12.60
Purchase #2	$39.85	8.446%	$43.2157	$43.22	$43.20	$43.20
Purchase #3	$31.29	6.489%	$33.3204	$33.32	$33.30	$33.30
Purchase #4	$140.84	8.602%	$152.9551	$152.96	$152.95	$153.00
Purchase #5	$142.60	4.787%	$149.4263	$149.43	$149.45	$149.40
Purchase #6	$58.50	5.311%	$61.6069	$61.61	$61.60	$61.60
Purchase #7	$67.72	7.166%	$72.5728	$72.57	$72.55	$72.60
7 purchase totals =	$492.74		$525.6999	$525.71	$525.65	$525.70