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	$155.62	8.314%	$168.5582	$168.56	$168.55	$168.60
Purchase #2	$91.75	8.208%	$99.2808	$99.28	$99.30	$99.30
Purchase #3	$231.30	7.356%	$248.3144	$248.31	$248.30	$248.30
Purchase #4	$136.64	11.691%	$152.6146	$152.61	$152.60	$152.60
Purchase #5	$91.93	4.803%	$96.3454	$96.35	$96.35	$96.30
Purchase #6	$53.72	3.843%	$55.7845	$55.78	$55.80	$55.80
Purchase #7	$38.26	3.184%	$39.4782	$39.48	$39.50	$39.50
7 purchase totals =	$799.22		$860.3761	$860.37	$860.40	$860.40