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	$80.38	13.714%	$91.4033	$91.40	$91.40	$91.40
Purchase #2	$79.52	13.331%	$90.1208	$90.12	$90.10	$90.10
Purchase #3	$184.68	3.236%	$190.6562	$190.66	$190.65	$190.70
Purchase #4	$138.34	4.710%	$144.8558	$144.86	$144.85	$144.90
Purchase #5	$112.63	4.628%	$117.8425	$117.84	$117.85	$117.80
Purchase #6	$236.47	10.308%	$260.8453	$260.85	$260.85	$260.80
Purchase #7	$190.72	13.510%	$216.4863	$216.49	$216.50	$216.50
7 purchase totals =	$1,022.74		$1,112.2102	$1,112.22	$1,112.20	$1,112.20