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	$116.33	4.279%	$121.3078	$121.31	$121.30	$121.30
Purchase #2	$56.94	11.133%	$63.2791	$63.28	$63.30	$63.30
Purchase #3	$241.75	13.376%	$274.0865	$274.09	$274.10	$274.10
Purchase #4	$131.65	12.850%	$148.567	$148.57	$148.55	$148.60
Purchase #5	$85.48	5.151%	$89.8831	$89.88	$89.90	$89.90
Purchase #6	$233.47	4.642%	$244.3077	$244.31	$244.30	$244.30
Purchase #7	$88.59	10.455%	$97.8521	$97.85	$97.85	$97.90
7 purchase totals =	$954.21		$1,039.2833	$1,039.29	$1,039.30	$1,039.40