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	$61.31	11.181%	$68.1651	$68.17	$68.15	$68.20
Purchase #2	$28.56	8.389%	$30.9559	$30.96	$30.95	$31.00
Purchase #3	$194.53	11.223%	$216.3621	$216.36	$216.35	$216.40
Purchase #4	$197.31	12.635%	$222.2401	$222.24	$222.25	$222.20
Purchase #5	$113.33	11.661%	$126.5454	$126.55	$126.55	$126.50
Purchase #6	$162.39	10.776%	$179.8891	$179.89	$179.90	$179.90
Purchase #7	$98.78	4.590%	$103.314	$103.31	$103.30	$103.30
7 purchase totals =	$856.21		$947.4717	$947.48	$947.45	$947.50