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	$220.96	12.858%	$249.371	$249.37	$249.35	$249.40
Purchase #2	$115.85	13.139%	$131.0715	$131.07	$131.05	$131.10
Purchase #3	$205.41	3.785%	$213.1848	$213.18	$213.20	$213.20
Purchase #4	$201.40	13.156%	$227.8962	$227.90	$227.90	$227.90
Purchase #5	$98.79	7.173%	$105.8762	$105.88	$105.90	$105.90
Purchase #6	$22.50	7.758%	$24.2456	$24.25	$24.25	$24.20
Purchase #7	$136.76	4.671%	$143.1481	$143.15	$143.15	$143.10
7 purchase totals =	$1,001.67		$1,094.7934	$1,094.80	$1,094.80	$1,094.80