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	$79.50	9.333%	$86.9197	$86.92	$86.90	$86.90
Purchase #2	$92.94	5.254%	$97.8231	$97.82	$97.80	$97.80
Purchase #3	$212.95	13.605%	$241.9218	$241.92	$241.90	$241.90
Purchase #4	$201.92	6.437%	$214.9176	$214.92	$214.90	$214.90
Purchase #5	$74.33	5.296%	$78.2665	$78.27	$78.25	$78.30
Purchase #6	$71.71	9.507%	$78.5275	$78.53	$78.55	$78.50
Purchase #7	$184.29	8.123%	$199.2599	$199.26	$199.25	$199.30
7 purchase totals =	$917.64		$997.6361	$997.64	$997.55	$997.60