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	$228.27	12.604%	$257.0412	$257.04	$257.05	$257.00
Purchase #2	$84.54	3.294%	$87.3247	$87.32	$87.30	$87.30
Purchase #3	$232.84	13.397%	$264.0336	$264.03	$264.05	$264.00
Purchase #4	$198.56	12.579%	$223.5369	$223.54	$223.55	$223.50
Purchase #5	$24.47	11.689%	$27.3303	$27.33	$27.35	$27.30
Purchase #6	$98.43	13.714%	$111.9287	$111.93	$111.95	$111.90
Purchase #7	$186.26	11.790%	$208.2201	$208.22	$208.20	$208.20
7 purchase totals =	$1,053.37		$1,179.4155	$1,179.41	$1,179.45	$1,179.20