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	$13.92	7.527%	$14.9678	$14.97	$14.95	$15.00
Purchase #2	$113.37	13.262%	$128.4051	$128.41	$128.40	$128.40
Purchase #3	$191.32	13.365%	$216.8899	$216.89	$216.90	$216.90
Purchase #4	$67.89	6.645%	$72.4013	$72.40	$72.40	$72.40
Purchase #5	$23.98	13.460%	$27.2077	$27.21	$27.20	$27.20
Purchase #6	$115.76	7.503%	$124.4455	$124.45	$124.45	$124.40
Purchase #7	$167.25	5.310%	$176.131	$176.13	$176.15	$176.10
7 purchase totals =	$693.49		$760.4483	$760.46	$760.45	$760.40