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	$102.63	12.541%	$115.5008	$115.50	$115.50	$115.50
Purchase #2	$36.87	13.791%	$41.9547	$41.95	$41.95	$42.00
Purchase #3	$122.98	4.393%	$128.3825	$128.38	$128.40	$128.40
Purchase #4	$177.41	7.626%	$190.9393	$190.94	$190.95	$190.90
Purchase #5	$77.37	10.358%	$85.384	$85.38	$85.40	$85.40
Purchase #6	$242.95	13.550%	$275.8697	$275.87	$275.85	$275.90
Purchase #7	$52.48	12.837%	$59.2169	$59.22	$59.20	$59.20
7 purchase totals =	$812.69		$897.2479	$897.24	$897.25	$897.30