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	$49.76	3.528%	$51.5155	$51.52	$51.50	$51.50
Purchase #2	$154.46	9.141%	$168.5792	$168.58	$168.60	$168.60
Purchase #3	$13.51	12.720%	$15.2285	$15.23	$15.25	$15.20
Purchase #4	$227.40	3.295%	$234.8928	$234.89	$234.90	$234.90
Purchase #5	$59.33	7.871%	$63.9999	$64.00	$64.00	$64.00
Purchase #6	$75.84	13.591%	$86.1474	$86.15	$86.15	$86.10
Purchase #7	$144.80	5.623%	$152.9421	$152.94	$152.95	$152.90
7 purchase totals =	$725.10		$773.3054	$773.31	$773.35	$773.20