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	$79.33	12.673%	$89.3835	$89.38	$89.40	$89.40
Purchase #2	$177.34	11.300%	$197.3794	$197.38	$197.40	$197.40
Purchase #3	$119.53	10.127%	$131.6348	$131.63	$131.65	$131.60
Purchase #4	$96.92	7.313%	$104.0078	$104.01	$104.00	$104.00
Purchase #5	$120.46	9.461%	$131.8567	$131.86	$131.85	$131.90
Purchase #6	$132.63	9.813%	$145.645	$145.65	$145.65	$145.60
Purchase #7	$161.86	13.478%	$183.6755	$183.68	$183.70	$183.70
7 purchase totals =	$888.07		$983.5827	$983.59	$983.65	$983.60