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	$49.40	4.388%	$51.5677	$51.57	$51.55	$51.60
Purchase #2	$36.55	7.424%	$39.2635	$39.26	$39.25	$39.30
Purchase #3	$131.86	10.669%	$145.9281	$145.93	$145.95	$145.90
Purchase #4	$10.56	9.508%	$11.564	$11.56	$11.55	$11.60
Purchase #5	$100.72	12.545%	$113.3553	$113.36	$113.35	$113.40
Purchase #6	$43.50	13.170%	$49.229	$49.23	$49.25	$49.20
Purchase #7	$82.61	3.751%	$85.7087	$85.71	$85.70	$85.70
7 purchase totals =	$455.20		$496.6163	$496.62	$496.60	$496.70