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	$31.27	6.438%	$33.2832	$33.28	$33.30	$33.30
Purchase #2	$165.47	3.351%	$171.0149	$171.01	$171.00	$171.00
Purchase #3	$139.74	13.307%	$158.3352	$158.34	$158.35	$158.30
Purchase #4	$69.43	12.724%	$78.2643	$78.26	$78.25	$78.30
Purchase #5	$143.98	4.402%	$150.318	$150.32	$150.30	$150.30
Purchase #6	$63.55	12.312%	$71.3743	$71.37	$71.35	$71.40
Purchase #7	$166.86	7.438%	$179.271	$179.27	$179.25	$179.30
7 purchase totals =	$780.30		$841.8609	$841.85	$841.80	$841.90