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	$182.69	3.668%	$189.3911	$189.39	$189.40	$189.40
Purchase #2	$119.71	8.740%	$130.1727	$130.17	$130.15	$130.20
Purchase #3	$178.34	10.105%	$196.3613	$196.36	$196.35	$196.40
Purchase #4	$129.60	8.189%	$140.2129	$140.21	$140.20	$140.20
Purchase #5	$172.60	3.285%	$178.2699	$178.27	$178.25	$178.30
Purchase #6	$80.82	8.300%	$87.5281	$87.53	$87.55	$87.50
Purchase #7	$150.70	7.754%	$162.3853	$162.39	$162.40	$162.40
7 purchase totals =	$1,014.46		$1,084.3213	$1,084.32	$1,084.30	$1,084.40