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	$20.84	12.688%	$23.4842	$23.48	$23.50	$23.50
Purchase #2	$172.39	13.686%	$195.9833	$195.98	$196.00	$196.00
Purchase #3	$196.51	8.293%	$212.8066	$212.81	$212.80	$212.80
Purchase #4	$109.30	3.547%	$113.1769	$113.18	$113.20	$113.20
Purchase #5	$29.33	6.780%	$31.3186	$31.32	$31.30	$31.30
Purchase #6	$81.31	13.164%	$92.0136	$92.01	$92.00	$92.00
Purchase #7	$185.84	5.511%	$196.0816	$196.08	$196.10	$196.10
7 purchase totals =	$795.52		$864.8648	$864.86	$864.90	$864.90