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	$139.27	12.164%	$156.2108	$156.21	$156.20	$156.20
Purchase #2	$54.56	9.160%	$59.5577	$59.56	$59.55	$59.60
Purchase #3	$220.61	11.608%	$246.2184	$246.22	$246.20	$246.20
Purchase #4	$171.52	3.358%	$177.2796	$177.28	$177.30	$177.30
Purchase #5	$14.67	4.698%	$15.3592	$15.36	$15.35	$15.40
Purchase #6	$113.50	9.582%	$124.3756	$124.38	$124.40	$124.40
Purchase #7	$82.59	12.470%	$92.889	$92.89	$92.90	$92.90
7 purchase totals =	$796.72		$871.8903	$871.90	$871.90	$872.00