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	$14.69	3.706%	$15.2344	$15.23	$15.25	$15.20
Purchase #2	$29.84	9.376%	$32.6378	$32.64	$32.65	$32.60
Purchase #3	$140.91	11.327%	$156.8709	$156.87	$156.85	$156.90
Purchase #4	$246.61	10.706%	$273.0121	$273.01	$273.00	$273.00
Purchase #5	$27.87	5.774%	$29.4792	$29.48	$29.50	$29.50
Purchase #6	$72.47	8.806%	$78.8517	$78.85	$78.85	$78.90
Purchase #7	$189.95	4.386%	$198.2812	$198.28	$198.30	$198.30
7 purchase totals =	$722.34		$784.3673	$784.36	$784.40	$784.40