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	$40.85	4.807%	$42.8137	$42.81	$42.80	$42.80
Purchase #2	$117.70	9.738%	$129.1616	$129.16	$129.15	$129.20
Purchase #3	$91.89	13.488%	$104.2841	$104.28	$104.30	$104.30
Purchase #4	$40.37	12.235%	$45.3093	$45.31	$45.30	$45.30
Purchase #5	$96.46	3.427%	$99.7657	$99.77	$99.75	$99.80
Purchase #6	$215.42	10.660%	$238.3838	$238.38	$238.40	$238.40
Purchase #7	$119.93	4.444%	$125.2597	$125.26	$125.25	$125.30
7 purchase totals =	$722.62		$784.9779	$784.97	$784.95	$785.10