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	$87.44	3.588%	$90.5773	$90.58	$90.60	$90.60
Purchase #2	$78.67	13.565%	$89.3416	$89.34	$89.35	$89.30
Purchase #3	$171.92	3.548%	$178.0197	$178.02	$178.00	$178.00
Purchase #4	$18.73	9.443%	$20.4987	$20.50	$20.50	$20.50
Purchase #5	$133.62	12.179%	$149.8936	$149.89	$149.90	$149.90
Purchase #6	$105.91	4.403%	$110.5732	$110.57	$110.55	$110.60
Purchase #7	$9.69	4.305%	$10.1072	$10.11	$10.10	$10.10
7 purchase totals =	$605.98		$649.0113	$649.01	$649.00	$649.00