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	$94.77	10.599%	$104.8147	$104.81	$104.80	$104.80
Purchase #2	$61.25	10.305%	$67.5618	$67.56	$67.55	$67.60
Purchase #3	$84.41	6.151%	$89.6021	$89.60	$89.60	$89.60
Purchase #4	$31.77	5.862%	$33.6324	$33.63	$33.65	$33.60
Purchase #5	$169.88	4.719%	$177.8966	$177.90	$177.90	$177.90
Purchase #6	$161.80	4.642%	$169.3108	$169.31	$169.30	$169.30
Purchase #7	$22.95	9.596%	$25.1523	$25.15	$25.15	$25.20
7 purchase totals =	$626.83		$667.9707	$667.96	$667.95	$668.00