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	$7.79	12.538%	$8.7667	$8.77	$8.75	$8.80
Purchase #2	$218.90	4.873%	$229.567	$229.57	$229.55	$229.60
Purchase #3	$119.77	7.496%	$128.748	$128.75	$128.75	$128.70
Purchase #4	$44.83	7.557%	$48.2178	$48.22	$48.20	$48.20
Purchase #5	$78.82	4.806%	$82.6081	$82.61	$82.60	$82.60
Purchase #6	$11.90	8.706%	$12.936	$12.94	$12.95	$12.90
Purchase #7	$93.78	6.417%	$99.7979	$99.80	$99.80	$99.80
7 purchase totals =	$575.79		$610.6415	$610.66	$610.60	$610.60