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	$19.71	7.441%	$21.1766	$21.18	$21.20	$21.20
Purchase #2	$51.57	3.566%	$53.409	$53.41	$53.40	$53.40
Purchase #3	$204.29	8.869%	$222.4085	$222.41	$222.40	$222.40
Purchase #4	$41.29	3.179%	$42.6026	$42.60	$42.60	$42.60
Purchase #5	$184.67	5.873%	$195.5157	$195.52	$195.50	$195.50
Purchase #6	$7.36	5.190%	$7.742	$7.74	$7.75	$7.70
Purchase #7	$122.97	3.818%	$127.665	$127.67	$127.65	$127.70
7 purchase totals =	$631.86		$670.5194	$670.53	$670.50	$670.50