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	$37.30	11.529%	$41.6003	$41.60	$41.60	$41.60
Purchase #2	$172.86	10.397%	$190.8323	$190.83	$190.85	$190.80
Purchase #3	$77.80	10.320%	$85.829	$85.83	$85.85	$85.80
Purchase #4	$68.98	8.742%	$75.0102	$75.01	$75.00	$75.00
Purchase #5	$59.40	9.758%	$65.1963	$65.20	$65.20	$65.20
Purchase #6	$200.84	4.356%	$209.5886	$209.59	$209.60	$209.60
Purchase #7	$224.47	5.268%	$236.2951	$236.30	$236.30	$236.30
7 purchase totals =	$841.65		$904.3518	$904.36	$904.40	$904.30