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	$146.47	5.309%	$154.2461	$154.25	$154.25	$154.20
Purchase #2	$189.38	13.804%	$215.522	$215.52	$215.50	$215.50
Purchase #3	$76.79	7.139%	$82.272	$82.27	$82.25	$82.30
Purchase #4	$32.98	7.620%	$35.4931	$35.49	$35.50	$35.50
Purchase #5	$189.46	4.294%	$197.5954	$197.60	$197.60	$197.60
Purchase #6	$31.52	7.365%	$33.8414	$33.84	$33.85	$33.80
Purchase #7	$92.65	3.193%	$95.6083	$95.61	$95.60	$95.60
7 purchase totals =	$759.25		$814.5783	$814.58	$814.55	$814.50