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	$64.30	12.604%	$72.4044	$72.40	$72.40	$72.40
Purchase #2	$232.90	11.628%	$259.9816	$259.98	$260.00	$260.00
Purchase #3	$18.97	9.543%	$20.7803	$20.78	$20.80	$20.80
Purchase #4	$222.87	5.842%	$235.8901	$235.89	$235.90	$235.90
Purchase #5	$79.92	4.306%	$83.3614	$83.36	$83.35	$83.40
Purchase #6	$52.62	9.224%	$57.4737	$57.47	$57.45	$57.50
Purchase #7	$171.96	11.366%	$191.505	$191.51	$191.50	$191.50
7 purchase totals =	$843.54		$921.3965	$921.39	$921.40	$921.50