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	$127.87	3.156%	$131.9056	$131.91	$131.90	$131.90
Purchase #2	$200.85	10.544%	$222.0276	$222.03	$222.05	$222.00
Purchase #3	$80.67	9.258%	$88.1384	$88.14	$88.15	$88.10
Purchase #4	$228.98	9.161%	$249.9569	$249.96	$249.95	$250.00
Purchase #5	$11.70	12.198%	$13.1272	$13.13	$13.15	$13.10
Purchase #6	$170.60	11.669%	$190.5073	$190.51	$190.50	$190.50
Purchase #7	$45.90	7.353%	$49.275	$49.28	$49.30	$49.30
7 purchase totals =	$866.57		$944.9380	$944.96	$945.00	$944.90