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	$30.72	8.617%	$33.3671	$33.37	$33.35	$33.40
Purchase #2	$28.54	8.358%	$30.9254	$30.93	$30.95	$30.90
Purchase #3	$164.69	13.423%	$186.7963	$186.80	$186.80	$186.80
Purchase #4	$204.40	7.594%	$219.9221	$219.92	$219.90	$219.90
Purchase #5	$233.59	8.869%	$254.3071	$254.31	$254.30	$254.30
Purchase #6	$82.55	11.824%	$92.3107	$92.31	$92.30	$92.30
Purchase #7	$57.57	3.346%	$59.4963	$59.50	$59.50	$59.50
7 purchase totals =	$802.06		$877.1250	$877.14	$877.10	$877.10