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	$53.60	5.347%	$56.466	$56.47	$56.45	$56.50
Purchase #2	$79.50	9.133%	$86.7607	$86.76	$86.75	$86.80
Purchase #3	$36.47	3.732%	$37.8311	$37.83	$37.85	$37.80
Purchase #4	$51.54	11.595%	$57.5161	$57.52	$57.50	$57.50
Purchase #5	$222.43	10.316%	$245.3759	$245.38	$245.40	$245.40
Purchase #6	$72.48	10.213%	$79.8824	$79.88	$79.90	$79.90
Purchase #7	$133.27	6.527%	$141.9685	$141.97	$141.95	$142.00
7 purchase totals =	$649.29		$705.8007	$705.81	$705.80	$705.90