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	$29.32	8.797%	$31.8993	$31.90	$31.90	$31.90
Purchase #2	$78.97	3.861%	$82.019	$82.02	$82.00	$82.00
Purchase #3	$94.77	7.249%	$101.6399	$101.64	$101.65	$101.60
Purchase #4	$107.33	11.665%	$119.85	$119.85	$119.85	$119.90
Purchase #5	$51.68	5.570%	$54.5586	$54.56	$54.55	$54.60
Purchase #6	$139.88	11.624%	$156.1397	$156.14	$156.15	$156.10
Purchase #7	$26.59	8.415%	$28.8275	$28.83	$28.85	$28.80
7 purchase totals =	$528.54		$574.9340	$574.94	$574.95	$574.90