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	$124.52	12.554%	$140.1522	$140.15	$140.15	$140.20
Purchase #2	$110.26	4.432%	$115.1467	$115.15	$115.15	$115.10
Purchase #3	$74.28	5.645%	$78.4731	$78.47	$78.45	$78.50
Purchase #4	$248.65	6.617%	$265.1032	$265.10	$265.10	$265.10
Purchase #5	$38.85	7.185%	$41.6414	$41.64	$41.65	$41.60
Purchase #6	$151.56	11.452%	$168.9167	$168.92	$168.90	$168.90
Purchase #7	$151.55	11.169%	$168.4766	$168.48	$168.50	$168.50
7 purchase totals =	$899.67		$977.9099	$977.91	$977.90	$977.90