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	$159.31	8.561%	$172.9485	$172.95	$172.95	$172.90
Purchase #2	$192.30	7.537%	$206.7937	$206.79	$206.80	$206.80
Purchase #3	$76.74	9.220%	$83.8154	$83.82	$83.80	$83.80
Purchase #4	$30.87	6.527%	$32.8849	$32.88	$32.90	$32.90
Purchase #5	$36.34	13.164%	$41.1238	$41.12	$41.10	$41.10
Purchase #6	$76.43	5.837%	$80.8912	$80.89	$80.90	$80.90
Purchase #7	$205.50	13.520%	$233.2836	$233.28	$233.30	$233.30
7 purchase totals =	$777.49		$851.7411	$851.73	$851.75	$851.70