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	$99.44	12.274%	$111.6453	$111.65	$111.65	$111.60
Purchase #2	$16.26	9.173%	$17.7515	$17.75	$17.75	$17.80
Purchase #3	$55.80	6.209%	$59.2646	$59.26	$59.25	$59.30
Purchase #4	$106.77	5.799%	$112.9616	$112.96	$112.95	$113.00
Purchase #5	$75.96	8.687%	$82.5586	$82.56	$82.55	$82.60
Purchase #6	$96.83	9.503%	$106.0318	$106.03	$106.05	$106.00
Purchase #7	$38.69	5.113%	$40.6682	$40.67	$40.65	$40.70
7 purchase totals =	$489.75		$530.8816	$530.88	$530.85	$531.00