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	$91.62	7.333%	$98.3385	$98.34	$98.35	$98.30
Purchase #2	$141.25	10.319%	$155.8256	$155.83	$155.85	$155.80
Purchase #3	$161.33	12.661%	$181.756	$181.76	$181.75	$181.80
Purchase #4	$123.46	6.180%	$131.0898	$131.09	$131.10	$131.10
Purchase #5	$202.64	9.619%	$222.1319	$222.13	$222.15	$222.10
Purchase #6	$209.60	11.124%	$232.9159	$232.92	$232.90	$232.90
Purchase #7	$136.69	10.315%	$150.7896	$150.79	$150.80	$150.80
7 purchase totals =	$1,066.59		$1,172.8473	$1,172.86	$1,172.90	$1,172.80