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	$39.29	6.188%	$41.7213	$41.72	$41.70	$41.70
Purchase #2	$75.55	9.508%	$82.7333	$82.73	$82.75	$82.70
Purchase #3	$131.88	5.518%	$139.1571	$139.16	$139.15	$139.20
Purchase #4	$225.25	6.709%	$240.362	$240.36	$240.35	$240.40
Purchase #5	$224.50	10.624%	$248.3509	$248.35	$248.35	$248.40
Purchase #6	$132.35	5.697%	$139.89	$139.89	$139.90	$139.90
Purchase #7	$33.36	7.783%	$35.9564	$35.96	$35.95	$36.00
7 purchase totals =	$862.18		$928.1710	$928.17	$928.15	$928.30