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	$73.85	12.240%	$82.8892	$82.89	$82.90	$82.90
Purchase #2	$136.58	5.129%	$143.5852	$143.59	$143.60	$143.60
Purchase #3	$71.34	9.343%	$78.0053	$78.01	$78.00	$78.00
Purchase #4	$206.73	4.607%	$216.2541	$216.25	$216.25	$216.30
Purchase #5	$29.49	6.292%	$31.3455	$31.35	$31.35	$31.30
Purchase #6	$64.58	8.111%	$69.8181	$69.82	$69.80	$69.80
Purchase #7	$29.74	7.396%	$31.9396	$31.94	$31.95	$31.90
7 purchase totals =	$612.31		$653.8370	$653.85	$653.85	$653.80