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	$31.62	7.251%	$33.9128	$33.91	$33.90	$33.90
Purchase #2	$224.45	5.770%	$237.4008	$237.40	$237.40	$237.40
Purchase #3	$41.87	8.682%	$45.5052	$45.51	$45.50	$45.50
Purchase #4	$84.31	7.674%	$90.7799	$90.78	$90.80	$90.80
Purchase #5	$90.34	11.734%	$100.9405	$100.94	$100.95	$100.90
Purchase #6	$191.70	13.601%	$217.7731	$217.77	$217.75	$217.80
Purchase #7	$204.37	6.630%	$217.9197	$217.92	$217.90	$217.90
7 purchase totals =	$868.66		$944.2320	$944.23	$944.20	$944.20