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	$190.89	10.111%	$210.1909	$210.19	$210.20	$210.20
Purchase #2	$104.29	12.166%	$116.9779	$116.98	$117.00	$117.00
Purchase #3	$73.36	6.770%	$78.3265	$78.33	$78.35	$78.30
Purchase #4	$95.83	13.257%	$108.5342	$108.53	$108.55	$108.50
Purchase #5	$96.41	5.808%	$102.0095	$102.01	$102.00	$102.00
Purchase #6	$52.84	12.180%	$59.2759	$59.28	$59.30	$59.30
Purchase #7	$246.47	3.426%	$254.9141	$254.91	$254.90	$254.90
7 purchase totals =	$860.09		$930.2290	$930.23	$930.30	$930.20