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	$127.79	6.874%	$136.5743	$136.57	$136.55	$136.60
Purchase #2	$42.77	9.343%	$46.766	$46.77	$46.75	$46.80
Purchase #3	$59.54	6.633%	$63.4893	$63.49	$63.50	$63.50
Purchase #4	$86.96	7.630%	$93.595	$93.60	$93.60	$93.60
Purchase #5	$83.56	4.595%	$87.3996	$87.40	$87.40	$87.40
Purchase #6	$238.36	12.614%	$268.4267	$268.43	$268.45	$268.40
Purchase #7	$52.37	13.828%	$59.6117	$59.61	$59.60	$59.60
7 purchase totals =	$691.35		$755.8626	$755.87	$755.85	$755.90