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	$109.87	13.628%	$124.8431	$124.84	$124.85	$124.80
Purchase #2	$227.63	6.870%	$243.2682	$243.27	$243.25	$243.30
Purchase #3	$51.92	10.761%	$57.5071	$57.51	$57.50	$57.50
Purchase #4	$82.83	6.365%	$88.1021	$88.10	$88.10	$88.10
Purchase #5	$195.94	11.266%	$218.0146	$218.01	$218.00	$218.00
Purchase #6	$153.88	9.714%	$168.8279	$168.83	$168.85	$168.80
Purchase #7	$123.86	13.128%	$140.1203	$140.12	$140.10	$140.10
7 purchase totals =	$945.93		$1,040.6833	$1,040.68	$1,040.65	$1,040.60