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	$40.99	6.822%	$43.7863	$43.79	$43.80	$43.80
Purchase #2	$33.45	4.507%	$34.9576	$34.96	$34.95	$35.00
Purchase #3	$57.39	3.664%	$59.4928	$59.49	$59.50	$59.50
Purchase #4	$94.34	12.138%	$105.791	$105.79	$105.80	$105.80
Purchase #5	$79.99	11.744%	$89.384	$89.38	$89.40	$89.40
Purchase #6	$101.94	3.701%	$105.7128	$105.71	$105.70	$105.70
Purchase #7	$97.73	5.702%	$103.3026	$103.30	$103.30	$103.30
7 purchase totals =	$505.83		$542.4271	$542.42	$542.45	$542.50