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	$117.88	11.418%	$131.3395	$131.34	$131.35	$131.30
Purchase #2	$244.44	11.647%	$272.9099	$272.91	$272.90	$272.90
Purchase #3	$197.41	11.694%	$220.4951	$220.50	$220.50	$220.50
Purchase #4	$81.40	9.840%	$89.4098	$89.41	$89.40	$89.40
Purchase #5	$33.48	13.537%	$38.0122	$38.01	$38.00	$38.00
Purchase #6	$224.40	9.560%	$245.8526	$245.85	$245.85	$245.90
Purchase #7	$32.67	10.541%	$36.1137	$36.11	$36.10	$36.10
7 purchase totals =	$931.68		$1,034.1328	$1,034.13	$1,034.10	$1,034.10