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	$115.44	13.505%	$131.0302	$131.03	$131.05	$131.00
Purchase #2	$168.51	13.284%	$190.8949	$190.89	$190.90	$190.90
Purchase #3	$39.83	12.751%	$44.9087	$44.91	$44.90	$44.90
Purchase #4	$157.61	8.485%	$170.9832	$170.98	$171.00	$171.00
Purchase #5	$18.68	5.802%	$19.7638	$19.76	$19.75	$19.80
Purchase #6	$50.34	10.395%	$55.5728	$55.57	$55.55	$55.60
Purchase #7	$88.43	12.513%	$99.4952	$99.50	$99.50	$99.50
7 purchase totals =	$638.84		$712.6488	$712.64	$712.65	$712.70