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	$16.90	11.513%	$18.8457	$18.85	$18.85	$18.80
Purchase #2	$47.34	8.143%	$51.1949	$51.19	$51.20	$51.20
Purchase #3	$72.78	6.451%	$77.475	$77.48	$77.50	$77.50
Purchase #4	$164.56	13.196%	$186.2753	$186.28	$186.30	$186.30
Purchase #5	$85.41	4.512%	$89.2637	$89.26	$89.25	$89.30
Purchase #6	$24.98	7.484%	$26.8495	$26.85	$26.85	$26.80
Purchase #7	$154.64	9.630%	$169.5318	$169.53	$169.55	$169.50
7 purchase totals =	$566.61		$619.4359	$619.44	$619.50	$619.40