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	$165.48	3.339%	$171.0054	$171.01	$171.00	$171.00
Purchase #2	$119.99	9.535%	$131.431	$131.43	$131.45	$131.40
Purchase #3	$124.41	5.357%	$131.0746	$131.07	$131.05	$131.10
Purchase #4	$40.85	3.388%	$42.234	$42.23	$42.25	$42.20
Purchase #5	$226.48	7.595%	$243.6812	$243.68	$243.70	$243.70
Purchase #6	$37.69	12.141%	$42.2659	$42.27	$42.25	$42.30
Purchase #7	$82.25	8.308%	$89.0833	$89.08	$89.10	$89.10
7 purchase totals =	$797.15		$850.7754	$850.77	$850.80	$850.80