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	$209.56	7.775%	$225.8533	$225.85	$225.85	$225.90
Purchase #2	$58.72	12.308%	$65.9473	$65.95	$65.95	$65.90
Purchase #3	$206.69	6.250%	$219.6081	$219.61	$219.60	$219.60
Purchase #4	$180.41	10.846%	$199.9773	$199.98	$200.00	$200.00
Purchase #5	$220.66	10.291%	$243.3681	$243.37	$243.35	$243.40
Purchase #6	$75.88	9.826%	$83.336	$83.34	$83.35	$83.30
Purchase #7	$91.66	10.324%	$101.123	$101.12	$101.10	$101.10
7 purchase totals =	$1,043.58		$1,139.2131	$1,139.22	$1,139.20	$1,139.20