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	$35.47	8.507%	$38.4874	$38.49	$38.50	$38.50
Purchase #2	$6.97	7.801%	$7.5137	$7.51	$7.50	$7.50
Purchase #3	$135.31	6.253%	$143.7709	$143.77	$143.75	$143.80
Purchase #4	$80.57	4.718%	$84.3713	$84.37	$84.35	$84.40
Purchase #5	$45.98	9.475%	$50.3366	$50.34	$50.35	$50.30
Purchase #6	$28.79	8.719%	$31.3002	$31.30	$31.30	$31.30
Purchase #7	$90.53	11.448%	$100.8939	$100.89	$100.90	$100.90
7 purchase totals =	$423.62		$456.6740	$456.67	$456.65	$456.70