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	$81.82	4.123%	$85.1934	$85.19	$85.20	$85.20
Purchase #2	$25.57	10.147%	$28.1646	$28.16	$28.15	$28.20
Purchase #3	$131.33	4.742%	$137.5577	$137.56	$137.55	$137.60
Purchase #4	$69.60	4.357%	$72.6325	$72.63	$72.65	$72.60
Purchase #5	$177.63	7.244%	$190.4975	$190.50	$190.50	$190.50
Purchase #6	$206.34	9.592%	$226.1321	$226.13	$226.15	$226.10
Purchase #7	$243.50	8.126%	$263.2868	$263.29	$263.30	$263.30
7 purchase totals =	$935.79		$1,003.4646	$1,003.46	$1,003.50	$1,003.50