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	$42.76	9.294%	$46.7341	$46.73	$46.75	$46.70
Purchase #2	$83.74	3.244%	$86.4565	$86.46	$86.45	$86.50
Purchase #3	$110.32	11.808%	$123.3466	$123.35	$123.35	$123.30
Purchase #4	$116.40	9.418%	$127.3626	$127.36	$127.35	$127.40
Purchase #5	$69.36	4.110%	$72.2107	$72.21	$72.20	$72.20
Purchase #6	$173.70	13.248%	$196.7118	$196.71	$196.70	$196.70
Purchase #7	$186.77	10.652%	$206.6647	$206.66	$206.65	$206.70
7 purchase totals =	$783.05		$859.4870	$859.48	$859.45	$859.50