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	$89.25	5.790%	$94.4176	$94.42	$94.40	$94.40
Purchase #2	$100.66	4.133%	$104.8203	$104.82	$104.80	$104.80
Purchase #3	$37.51	7.561%	$40.3461	$40.35	$40.35	$40.30
Purchase #4	$21.73	10.756%	$24.0673	$24.07	$24.05	$24.10
Purchase #5	$63.32	12.246%	$71.0742	$71.07	$71.05	$71.10
Purchase #6	$123.90	12.330%	$139.1769	$139.18	$139.20	$139.20
Purchase #7	$206.40	4.629%	$215.9543	$215.95	$215.95	$216.00
7 purchase totals =	$642.77		$689.8567	$689.86	$689.80	$689.90