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	$32.94	12.800%	$37.1563	$37.16	$37.15	$37.20
Purchase #2	$83.64	7.472%	$89.8896	$89.89	$89.90	$89.90
Purchase #3	$208.75	6.794%	$222.9325	$222.93	$222.95	$222.90
Purchase #4	$240.33	8.575%	$260.9383	$260.94	$260.95	$260.90
Purchase #5	$89.60	9.291%	$97.9247	$97.92	$97.90	$97.90
Purchase #6	$113.83	12.636%	$128.2136	$128.21	$128.20	$128.20
Purchase #7	$18.52	8.258%	$20.0494	$20.05	$20.05	$20.00
7 purchase totals =	$787.61		$857.1044	$857.10	$857.10	$857.00