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	$210.44	11.267%	$234.1503	$234.15	$234.15	$234.20
Purchase #2	$233.79	5.610%	$246.9056	$246.91	$246.90	$246.90
Purchase #3	$18.84	8.196%	$20.3841	$20.38	$20.40	$20.40
Purchase #4	$31.95	13.572%	$36.2863	$36.29	$36.30	$36.30
Purchase #5	$159.50	12.228%	$179.0037	$179.00	$179.00	$179.00
Purchase #6	$28.58	13.219%	$32.358	$32.36	$32.35	$32.40
Purchase #7	$55.30	7.239%	$59.3032	$59.30	$59.30	$59.30
7 purchase totals =	$738.40		$808.3912	$808.39	$808.40	$808.50