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	$141.88	12.208%	$159.2007	$159.20	$159.20	$159.20
Purchase #2	$36.69	7.853%	$39.5713	$39.57	$39.55	$39.60
Purchase #3	$136.45	5.576%	$144.0585	$144.06	$144.05	$144.10
Purchase #4	$122.51	13.545%	$139.104	$139.10	$139.10	$139.10
Purchase #5	$183.96	6.666%	$196.2228	$196.22	$196.20	$196.20
Purchase #6	$246.59	7.271%	$264.5196	$264.52	$264.50	$264.50
Purchase #7	$89.72	6.632%	$95.6702	$95.67	$95.65	$95.70
7 purchase totals =	$957.80		$1,038.3471	$1,038.34	$1,038.25	$1,038.40