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	$33.39	12.551%	$37.5808	$37.58	$37.60	$37.60
Purchase #2	$134.25	5.844%	$142.0956	$142.10	$142.10	$142.10
Purchase #3	$198.30	7.474%	$213.1209	$213.12	$213.10	$213.10
Purchase #4	$36.50	12.825%	$41.1811	$41.18	$41.20	$41.20
Purchase #5	$197.34	13.265%	$223.5172	$223.52	$223.50	$223.50
Purchase #6	$108.36	3.153%	$111.7766	$111.78	$111.80	$111.80
Purchase #7	$147.47	11.465%	$164.3774	$164.38	$164.40	$164.40
7 purchase totals =	$855.61		$933.6496	$933.66	$933.70	$933.70