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	$59.62	13.438%	$67.6317	$67.63	$67.65	$67.60
Purchase #2	$29.43	5.337%	$31.0007	$31.00	$31.00	$31.00
Purchase #3	$154.91	8.813%	$168.5622	$168.56	$168.55	$168.60
Purchase #4	$171.99	9.339%	$188.0521	$188.05	$188.05	$188.10
Purchase #5	$83.73	7.241%	$89.7929	$89.79	$89.80	$89.80
Purchase #6	$72.61	13.799%	$82.6295	$82.63	$82.65	$82.60
Purchase #7	$189.39	13.104%	$214.2077	$214.21	$214.20	$214.20
7 purchase totals =	$761.68		$841.8768	$841.87	$841.90	$841.90