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	$51.86	10.400%	$57.2534	$57.25	$57.25	$57.30
Purchase #2	$206.48	11.460%	$230.1426	$230.14	$230.15	$230.10
Purchase #3	$57.54	3.266%	$59.4193	$59.42	$59.40	$59.40
Purchase #4	$227.39	12.309%	$255.3794	$255.38	$255.40	$255.40
Purchase #5	$237.98	13.829%	$270.8903	$270.89	$270.90	$270.90
Purchase #6	$34.63	3.497%	$35.841	$35.84	$35.85	$35.80
Purchase #7	$180.83	4.682%	$189.2965	$189.30	$189.30	$189.30
7 purchase totals =	$996.71		$1,098.2225	$1,098.22	$1,098.25	$1,098.20