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	$40.47	12.417%	$45.4952	$45.50	$45.50	$45.50
Purchase #2	$232.91	12.759%	$262.627	$262.63	$262.65	$262.60
Purchase #3	$74.59	4.195%	$77.7191	$77.72	$77.70	$77.70
Purchase #4	$160.32	4.656%	$167.7845	$167.78	$167.80	$167.80
Purchase #5	$128.26	13.188%	$145.1749	$145.17	$145.15	$145.20
Purchase #6	$64.98	3.619%	$67.3316	$67.33	$67.35	$67.30
Purchase #7	$204.89	4.282%	$213.6634	$213.66	$213.65	$213.70
7 purchase totals =	$906.42		$979.7957	$979.79	$979.80	$979.80