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	$122.32	11.640%	$136.558	$136.56	$136.55	$136.60
Purchase #2	$176.84	12.706%	$199.3093	$199.31	$199.30	$199.30
Purchase #3	$84.83	6.503%	$90.3465	$90.35	$90.35	$90.30
Purchase #4	$162.45	12.402%	$182.597	$182.60	$182.60	$182.60
Purchase #5	$141.90	7.742%	$152.8859	$152.89	$152.90	$152.90
Purchase #6	$199.75	6.138%	$212.0107	$212.01	$212.00	$212.00
Purchase #7	$174.41	7.395%	$187.3076	$187.31	$187.30	$187.30
7 purchase totals =	$1,062.50		$1,161.0150	$1,161.03	$1,161.00	$1,161.00