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	$38.28	11.755%	$42.7798	$42.78	$42.80	$42.80
Purchase #2	$95.94	9.709%	$105.2548	$105.25	$105.25	$105.30
Purchase #3	$124.37	6.606%	$132.5859	$132.59	$132.60	$132.60
Purchase #4	$144.77	11.740%	$161.766	$161.77	$161.75	$161.80
Purchase #5	$163.98	9.838%	$180.1124	$180.11	$180.10	$180.10
Purchase #6	$95.67	3.374%	$98.8979	$98.90	$98.90	$98.90
Purchase #7	$245.50	7.488%	$263.883	$263.88	$263.90	$263.90
7 purchase totals =	$908.51		$985.2798	$985.28	$985.30	$985.40