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	$143.71	8.295%	$155.6307	$155.63	$155.65	$155.60
Purchase #2	$148.27	5.794%	$156.8608	$156.86	$156.85	$156.90
Purchase #3	$167.62	12.148%	$187.9825	$187.98	$188.00	$188.00
Purchase #4	$11.43	4.360%	$11.9283	$11.93	$11.95	$11.90
Purchase #5	$100.80	11.139%	$112.0281	$112.03	$112.05	$112.00
Purchase #6	$34.44	3.291%	$35.5734	$35.57	$35.55	$35.60
Purchase #7	$183.52	4.560%	$191.8885	$191.89	$191.90	$191.90
7 purchase totals =	$789.79		$851.8923	$851.89	$851.95	$851.90