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	$113.32	6.360%	$120.5272	$120.53	$120.55	$120.50
Purchase #2	$109.33	9.156%	$119.3403	$119.34	$119.35	$119.30
Purchase #3	$126.42	8.484%	$137.1455	$137.15	$137.15	$137.10
Purchase #4	$140.45	8.820%	$152.8377	$152.84	$152.85	$152.80
Purchase #5	$161.83	5.801%	$171.2178	$171.22	$171.20	$171.20
Purchase #6	$209.94	8.712%	$228.23	$228.23	$228.25	$228.20
Purchase #7	$100.42	10.457%	$110.9209	$110.92	$110.90	$110.90
7 purchase totals =	$961.71		$1,040.2194	$1,040.23	$1,040.25	$1,040.00