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	$104.82	6.201%	$111.3199	$111.32	$111.30	$111.30
Purchase #2	$246.96	8.648%	$268.3171	$268.32	$268.30	$268.30
Purchase #3	$45.46	4.490%	$47.5012	$47.50	$47.50	$47.50
Purchase #4	$44.34	6.619%	$47.2749	$47.27	$47.25	$47.30
Purchase #5	$180.72	10.571%	$199.8239	$199.82	$199.80	$199.80
Purchase #6	$158.74	8.553%	$172.317	$172.32	$172.30	$172.30
Purchase #7	$225.88	13.239%	$255.7843	$255.78	$255.80	$255.80
7 purchase totals =	$1,006.92		$1,102.3383	$1,102.33	$1,102.25	$1,102.30