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	$166.88	12.185%	$187.2143	$187.21	$187.20	$187.20
Purchase #2	$69.73	12.641%	$78.5446	$78.54	$78.55	$78.50
Purchase #3	$248.53	3.337%	$256.8234	$256.82	$256.80	$256.80
Purchase #4	$147.96	12.752%	$166.8279	$166.83	$166.85	$166.80
Purchase #5	$7.93	3.814%	$8.2325	$8.23	$8.25	$8.20
Purchase #6	$26.90	4.738%	$28.1745	$28.17	$28.15	$28.20
Purchase #7	$28.32	10.256%	$31.2245	$31.22	$31.20	$31.20
7 purchase totals =	$696.25		$757.0417	$757.02	$757.00	$756.90