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	$185.97	11.611%	$207.563	$207.56	$207.55	$207.60
Purchase #2	$52.75	8.609%	$57.2912	$57.29	$57.30	$57.30
Purchase #3	$30.70	5.365%	$32.3471	$32.35	$32.35	$32.30
Purchase #4	$115.51	6.505%	$123.0239	$123.02	$123.00	$123.00
Purchase #5	$99.60	12.463%	$112.0131	$112.01	$112.00	$112.00
Purchase #6	$55.57	7.559%	$59.7705	$59.77	$59.75	$59.80
Purchase #7	$34.50	8.315%	$37.3687	$37.37	$37.35	$37.40
7 purchase totals =	$574.60		$629.3775	$629.37	$629.30	$629.40