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	$89.67	12.177%	$100.5891	$100.59	$100.60	$100.60
Purchase #2	$216.31	10.214%	$238.4039	$238.40	$238.40	$238.40
Purchase #3	$80.47	6.796%	$85.9387	$85.94	$85.95	$85.90
Purchase #4	$47.61	12.439%	$53.5322	$53.53	$53.55	$53.50
Purchase #5	$76.99	12.501%	$86.6145	$86.61	$86.60	$86.60
Purchase #6	$79.79	4.565%	$83.4324	$83.43	$83.45	$83.40
Purchase #7	$245.35	12.648%	$276.3819	$276.38	$276.40	$276.40
7 purchase totals =	$836.19		$924.8927	$924.88	$924.95	$924.80