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	$136.78	10.302%	$150.8711	$150.87	$150.85	$150.90
Purchase #2	$50.99	3.659%	$52.8557	$52.86	$52.85	$52.90
Purchase #3	$87.51	13.507%	$99.33	$99.33	$99.35	$99.30
Purchase #4	$236.54	13.508%	$268.4918	$268.49	$268.50	$268.50
Purchase #5	$88.46	7.280%	$94.8999	$94.90	$94.90	$94.90
Purchase #6	$12.52	6.368%	$13.3173	$13.32	$13.30	$13.30
Purchase #7	$215.69	8.474%	$233.9676	$233.97	$233.95	$234.00
7 purchase totals =	$828.49		$913.7334	$913.74	$913.70	$913.80