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	$234.69	3.474%	$242.8431	$242.84	$242.85	$242.80
Purchase #2	$41.58	13.615%	$47.2411	$47.24	$47.25	$47.20
Purchase #3	$86.41	13.805%	$98.3389	$98.34	$98.35	$98.30
Purchase #4	$58.29	6.265%	$61.9419	$61.94	$61.95	$61.90
Purchase #5	$100.33	12.144%	$112.5141	$112.51	$112.50	$112.50
Purchase #6	$49.84	11.686%	$55.6643	$55.66	$55.65	$55.70
Purchase #7	$35.43	13.828%	$40.3293	$40.33	$40.35	$40.30
7 purchase totals =	$606.57		$658.8727	$658.86	$658.90	$658.70