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	$28.30	12.709%	$31.8966	$31.90	$31.90	$31.90
Purchase #2	$80.63	11.474%	$89.8815	$89.88	$89.90	$89.90
Purchase #3	$212.29	8.280%	$229.8676	$229.87	$229.85	$229.90
Purchase #4	$34.33	9.253%	$37.5066	$37.51	$37.50	$37.50
Purchase #5	$17.99	12.188%	$20.1826	$20.18	$20.20	$20.20
Purchase #6	$197.64	8.693%	$214.8208	$214.82	$214.80	$214.80
Purchase #7	$183.45	13.645%	$208.4818	$208.48	$208.50	$208.50
7 purchase totals =	$754.63		$832.6375	$832.64	$832.65	$832.70