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	$60.76	12.744%	$68.5033	$68.50	$68.50	$68.50
Purchase #2	$203.39	9.844%	$223.4117	$223.41	$223.40	$223.40
Purchase #3	$33.81	7.703%	$36.4144	$36.41	$36.40	$36.40
Purchase #4	$232.69	10.400%	$256.8898	$256.89	$256.90	$256.90
Purchase #5	$133.38	8.649%	$144.916	$144.92	$144.90	$144.90
Purchase #6	$59.29	7.163%	$63.5369	$63.54	$63.55	$63.50
Purchase #7	$112.35	13.343%	$127.3409	$127.34	$127.35	$127.30
7 purchase totals =	$835.67		$921.0130	$921.01	$921.00	$920.90