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	$120.50	11.570%	$134.4419	$134.44	$134.45	$134.40
Purchase #2	$84.53	6.600%	$90.109	$90.11	$90.10	$90.10
Purchase #3	$66.41	8.296%	$71.9194	$71.92	$71.90	$71.90
Purchase #4	$150.51	9.375%	$164.6203	$164.62	$164.60	$164.60
Purchase #5	$7.57	5.448%	$7.9824	$7.98	$8.00	$8.00
Purchase #6	$125.78	8.708%	$136.7329	$136.73	$136.75	$136.70
Purchase #7	$81.59	7.623%	$87.8096	$87.81	$87.80	$87.80
7 purchase totals =	$636.89		$693.6155	$693.61	$693.60	$693.50