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	$41.29	4.171%	$43.0122	$43.01	$43.00	$43.00
Purchase #2	$219.47	3.651%	$227.4828	$227.48	$227.50	$227.50
Purchase #3	$100.51	8.689%	$109.2433	$109.24	$109.25	$109.20
Purchase #4	$88.58	12.557%	$99.703	$99.70	$99.70	$99.70
Purchase #5	$37.56	6.776%	$40.1051	$40.11	$40.10	$40.10
Purchase #6	$241.76	13.637%	$274.7288	$274.73	$274.75	$274.70
Purchase #7	$146.92	6.646%	$156.6843	$156.68	$156.70	$156.70
7 purchase totals =	$876.09		$950.9595	$950.95	$951.00	$950.90