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	$228.30	12.282%	$256.3398	$256.34	$256.35	$256.30
Purchase #2	$58.30	11.250%	$64.8588	$64.86	$64.85	$64.90
Purchase #3	$41.29	5.611%	$43.6068	$43.61	$43.60	$43.60
Purchase #4	$44.71	3.177%	$46.1304	$46.13	$46.15	$46.10
Purchase #5	$85.41	12.298%	$95.9137	$95.91	$95.90	$95.90
Purchase #6	$138.64	10.295%	$152.913	$152.91	$152.90	$152.90
Purchase #7	$73.25	9.827%	$80.4483	$80.45	$80.45	$80.40
7 purchase totals =	$669.90		$740.2108	$740.21	$740.20	$740.10