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	$163.97	13.329%	$185.8256	$185.83	$185.85	$185.80
Purchase #2	$6.49	6.238%	$6.8948	$6.89	$6.90	$6.90
Purchase #3	$86.67	13.421%	$98.302	$98.30	$98.30	$98.30
Purchase #4	$70.35	10.106%	$77.4596	$77.46	$77.45	$77.50
Purchase #5	$111.90	6.558%	$119.2384	$119.24	$119.25	$119.20
Purchase #6	$243.71	10.731%	$269.8625	$269.86	$269.85	$269.90
Purchase #7	$41.77	3.458%	$43.2144	$43.21	$43.20	$43.20
7 purchase totals =	$724.86		$800.7973	$800.79	$800.80	$800.80