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	$137.53	3.626%	$142.5168	$142.52	$142.50	$142.50
Purchase #2	$146.72	3.416%	$151.732	$151.73	$151.75	$151.70
Purchase #3	$151.81	7.148%	$162.6614	$162.66	$162.65	$162.70
Purchase #4	$242.54	3.420%	$250.8349	$250.83	$250.85	$250.80
Purchase #5	$148.45	3.374%	$153.4587	$153.46	$153.45	$153.50
Purchase #6	$216.59	12.149%	$242.9035	$242.90	$242.90	$242.90
Purchase #7	$75.96	5.663%	$80.2616	$80.26	$80.25	$80.30
7 purchase totals =	$1,119.60		$1,184.3689	$1,184.36	$1,184.35	$1,184.40