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	$63.98	10.179%	$70.4925	$70.49	$70.50	$70.50
Purchase #2	$196.96	6.816%	$210.3848	$210.38	$210.40	$210.40
Purchase #3	$124.76	7.681%	$134.3428	$134.34	$134.35	$134.30
Purchase #4	$79.52	12.297%	$89.2986	$89.30	$89.30	$89.30
Purchase #5	$112.38	12.544%	$126.4769	$126.48	$126.50	$126.50
Purchase #6	$24.45	13.257%	$27.6913	$27.69	$27.70	$27.70
Purchase #7	$153.54	11.150%	$170.6597	$170.66	$170.65	$170.70
7 purchase totals =	$755.59		$829.3466	$829.34	$829.40	$829.40