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	$92.33	8.579%	$100.251	$100.25	$100.25	$100.30
Purchase #2	$109.80	5.218%	$115.5294	$115.53	$115.55	$115.50
Purchase #3	$6.33	7.787%	$6.8229	$6.82	$6.80	$6.80
Purchase #4	$35.79	4.292%	$37.3261	$37.33	$37.35	$37.30
Purchase #5	$121.63	10.389%	$134.2661	$134.27	$134.25	$134.30
Purchase #6	$60.71	4.684%	$63.5537	$63.55	$63.55	$63.60
Purchase #7	$40.73	11.184%	$45.2852	$45.29	$45.30	$45.30
7 purchase totals =	$467.32		$503.0344	$503.04	$503.05	$503.10