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	$93.49	7.525%	$100.5251	$100.53	$100.55	$100.50
Purchase #2	$178.90	3.295%	$184.7948	$184.79	$184.80	$184.80
Purchase #3	$232.98	7.603%	$250.6935	$250.69	$250.70	$250.70
Purchase #4	$86.47	10.140%	$95.2381	$95.24	$95.25	$95.20
Purchase #5	$250.57	10.108%	$275.8976	$275.90	$275.90	$275.90
Purchase #6	$52.66	5.543%	$55.5789	$55.58	$55.60	$55.60
Purchase #7	$192.43	13.331%	$218.0828	$218.08	$218.10	$218.10
7 purchase totals =	$1,087.50		$1,180.8108	$1,180.81	$1,180.90	$1,180.80