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	$225.40	12.421%	$253.3969	$253.40	$253.40	$253.40
Purchase #2	$249.98	8.765%	$271.8907	$271.89	$271.90	$271.90
Purchase #3	$68.44	10.217%	$75.4325	$75.43	$75.45	$75.40
Purchase #4	$87.40	3.591%	$90.5385	$90.54	$90.55	$90.50
Purchase #5	$168.76	9.131%	$184.1695	$184.17	$184.15	$184.20
Purchase #6	$69.58	4.474%	$72.693	$72.69	$72.70	$72.70
Purchase #7	$29.80	6.551%	$31.7522	$31.75	$31.75	$31.80
7 purchase totals =	$899.36		$979.8733	$979.87	$979.90	$979.90