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	$170.46	11.477%	$190.0237	$190.02	$190.00	$190.00
Purchase #2	$248.55	9.631%	$272.4879	$272.49	$272.50	$272.50
Purchase #3	$164.48	13.329%	$186.4035	$186.40	$186.40	$186.40
Purchase #4	$155.41	5.719%	$164.2979	$164.30	$164.30	$164.30
Purchase #5	$83.61	13.682%	$95.0495	$95.05	$95.05	$95.00
Purchase #6	$103.31	9.557%	$113.1833	$113.18	$113.20	$113.20
Purchase #7	$100.89	8.839%	$109.8077	$109.81	$109.80	$109.80
7 purchase totals =	$1,026.71		$1,131.2535	$1,131.25	$1,131.25	$1,131.20