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	$37.87	13.256%	$42.89	$42.89	$42.90	$42.90
Purchase #2	$113.84	8.353%	$123.3491	$123.35	$123.35	$123.30
Purchase #3	$12.60	8.731%	$13.7001	$13.70	$13.70	$13.70
Purchase #4	$50.71	3.820%	$52.6471	$52.65	$52.65	$52.60
Purchase #5	$147.35	11.864%	$164.8316	$164.83	$164.85	$164.80
Purchase #6	$207.50	5.118%	$218.1199	$218.12	$218.10	$218.10
Purchase #7	$107.98	9.392%	$118.1215	$118.12	$118.10	$118.10
7 purchase totals =	$677.85		$733.6593	$733.66	$733.65	$733.50