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	$99.81	3.204%	$103.0079	$103.01	$103.00	$103.00
Purchase #2	$233.37	6.157%	$247.7386	$247.74	$247.75	$247.70
Purchase #3	$122.87	11.772%	$137.3343	$137.33	$137.35	$137.30
Purchase #4	$34.77	8.548%	$37.7421	$37.74	$37.75	$37.70
Purchase #5	$93.51	4.812%	$98.0097	$98.01	$98.00	$98.00
Purchase #6	$240.34	3.802%	$249.4777	$249.48	$249.50	$249.50
Purchase #7	$109.46	13.210%	$123.9197	$123.92	$123.90	$123.90
7 purchase totals =	$934.13		$997.2300	$997.23	$997.25	$997.10