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	$93.97	6.557%	$100.1316	$100.13	$100.15	$100.10
Purchase #2	$18.69	9.240%	$20.417	$20.42	$20.40	$20.40
Purchase #3	$199.59	9.120%	$217.7926	$217.79	$217.80	$217.80
Purchase #4	$228.43	4.425%	$238.538	$238.54	$238.55	$238.50
Purchase #5	$69.53	11.331%	$77.4084	$77.41	$77.40	$77.40
Purchase #6	$43.54	5.270%	$45.8346	$45.83	$45.85	$45.80
Purchase #7	$95.96	13.539%	$108.952	$108.95	$108.95	$109.00
7 purchase totals =	$749.71		$809.0742	$809.07	$809.10	$809.00