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	$138.88	4.284%	$144.8296	$144.83	$144.85	$144.80
Purchase #2	$218.90	5.755%	$231.4977	$231.50	$231.50	$231.50
Purchase #3	$40.47	4.222%	$42.1786	$42.18	$42.20	$42.20
Purchase #4	$72.77	5.661%	$76.8895	$76.89	$76.90	$76.90
Purchase #5	$209.87	4.776%	$219.8934	$219.89	$219.90	$219.90
Purchase #6	$126.77	5.168%	$133.3215	$133.32	$133.30	$133.30
Purchase #7	$171.28	4.654%	$179.2514	$179.25	$179.25	$179.30
7 purchase totals =	$978.94		$1,027.8617	$1,027.86	$1,027.90	$1,027.90