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	$56.80	5.519%	$59.9348	$59.93	$59.95	$59.90
Purchase #2	$35.67	9.813%	$39.1703	$39.17	$39.15	$39.20
Purchase #3	$167.64	7.810%	$180.7327	$180.73	$180.75	$180.70
Purchase #4	$230.29	8.814%	$250.5878	$250.59	$250.60	$250.60
Purchase #5	$176.33	7.695%	$189.8986	$189.90	$189.90	$189.90
Purchase #6	$116.86	6.537%	$124.4991	$124.50	$124.50	$124.50
Purchase #7	$142.25	11.707%	$158.9032	$158.90	$158.90	$158.90
7 purchase totals =	$925.84		$1,003.7265	$1,003.72	$1,003.75	$1,003.70