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	$239.46	8.571%	$259.9841	$259.98	$260.00	$260.00
Purchase #2	$224.52	6.364%	$238.8085	$238.81	$238.80	$238.80
Purchase #3	$96.77	9.794%	$106.2477	$106.25	$106.25	$106.20
Purchase #4	$76.61	13.561%	$86.9991	$87.00	$87.00	$87.00
Purchase #5	$78.79	4.289%	$82.1693	$82.17	$82.15	$82.20
Purchase #6	$205.34	13.146%	$232.334	$232.33	$232.35	$232.30
Purchase #7	$59.82	9.224%	$65.3378	$65.34	$65.35	$65.30
7 purchase totals =	$981.31		$1,071.8805	$1,071.88	$1,071.90	$1,071.80