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	$7.54	10.174%	$8.3071	$8.31	$8.30	$8.30
Purchase #2	$101.63	10.210%	$112.0064	$112.01	$112.00	$112.00
Purchase #3	$96.90	3.859%	$100.6394	$100.64	$100.65	$100.60
Purchase #4	$166.33	9.263%	$181.7371	$181.74	$181.75	$181.70
Purchase #5	$118.97	3.782%	$123.4694	$123.47	$123.45	$123.50
Purchase #6	$155.79	10.305%	$171.8442	$171.84	$171.85	$171.80
Purchase #7	$127.55	10.559%	$141.018	$141.02	$141.00	$141.00
7 purchase totals =	$774.71		$839.0216	$839.03	$839.00	$838.90