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	$235.84	9.167%	$257.4595	$257.46	$257.45	$257.50
Purchase #2	$196.61	6.797%	$209.9736	$209.97	$209.95	$210.00
Purchase #3	$211.36	7.704%	$227.6432	$227.64	$227.65	$227.60
Purchase #4	$56.59	5.639%	$59.7811	$59.78	$59.80	$59.80
Purchase #5	$126.98	9.862%	$139.5028	$139.50	$139.50	$139.50
Purchase #6	$141.31	3.511%	$146.2714	$146.27	$146.25	$146.30
Purchase #7	$55.84	6.529%	$59.4858	$59.49	$59.50	$59.50
7 purchase totals =	$1,024.53		$1,100.1174	$1,100.11	$1,100.10	$1,100.20