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	$33.93	6.135%	$36.0116	$36.01	$36.00	$36.00
Purchase #2	$145.89	12.742%	$164.4793	$164.48	$164.50	$164.50
Purchase #3	$28.98	13.554%	$32.9079	$32.91	$32.90	$32.90
Purchase #4	$10.79	11.363%	$12.0161	$12.02	$12.00	$12.00
Purchase #5	$102.43	10.144%	$112.8205	$112.82	$112.80	$112.80
Purchase #6	$46.59	13.357%	$52.813	$52.81	$52.80	$52.80
Purchase #7	$233.92	6.757%	$249.726	$249.73	$249.75	$249.70
7 purchase totals =	$602.53		$660.7744	$660.78	$660.75	$660.70