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	$244.74	12.497%	$275.3252	$275.33	$275.35	$275.30
Purchase #2	$22.59	13.571%	$25.6557	$25.66	$25.65	$25.70
Purchase #3	$212.89	5.636%	$224.8885	$224.89	$224.90	$224.90
Purchase #4	$182.33	5.154%	$191.7273	$191.73	$191.75	$191.70
Purchase #5	$102.44	10.251%	$112.9411	$112.94	$112.95	$112.90
Purchase #6	$96.53	3.618%	$100.0225	$100.02	$100.00	$100.00
Purchase #7	$208.48	5.532%	$220.0131	$220.01	$220.00	$220.00
7 purchase totals =	$1,070.00		$1,150.5734	$1,150.58	$1,150.60	$1,150.50