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	$28.94	9.573%	$31.7104	$31.71	$31.70	$31.70
Purchase #2	$45.72	9.593%	$50.1059	$50.11	$50.10	$50.10
Purchase #3	$62.90	8.472%	$68.2289	$68.23	$68.25	$68.20
Purchase #4	$177.94	12.666%	$200.4779	$200.48	$200.50	$200.50
Purchase #5	$148.79	7.416%	$159.8243	$159.82	$159.80	$159.80
Purchase #6	$213.78	7.131%	$229.0247	$229.02	$229.00	$229.00
Purchase #7	$41.85	9.694%	$45.9069	$45.91	$45.90	$45.90
7 purchase totals =	$719.92		$785.2790	$785.28	$785.25	$785.20