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	$36.98	11.781%	$41.3366	$41.34	$41.35	$41.30
Purchase #2	$162.86	13.723%	$185.2093	$185.21	$185.20	$185.20
Purchase #3	$127.70	12.380%	$143.5093	$143.51	$143.50	$143.50
Purchase #4	$7.80	5.535%	$8.2317	$8.23	$8.25	$8.20
Purchase #5	$81.50	12.761%	$91.9002	$91.90	$91.90	$91.90
Purchase #6	$42.86	9.233%	$46.8173	$46.82	$46.80	$46.80
Purchase #7	$168.74	11.284%	$187.7806	$187.78	$187.80	$187.80
7 purchase totals =	$628.44		$704.7850	$704.79	$704.80	$704.70