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	$138.78	12.510%	$156.1414	$156.14	$156.15	$156.10
Purchase #2	$107.53	11.807%	$120.2261	$120.23	$120.25	$120.20
Purchase #3	$79.82	13.224%	$90.3754	$90.38	$90.40	$90.40
Purchase #4	$67.35	7.599%	$72.4679	$72.47	$72.45	$72.50
Purchase #5	$186.27	12.499%	$209.5519	$209.55	$209.55	$209.60
Purchase #6	$212.66	4.808%	$222.8847	$222.88	$222.90	$222.90
Purchase #7	$73.31	7.147%	$78.5495	$78.55	$78.55	$78.50
7 purchase totals =	$865.72		$950.1969	$950.20	$950.25	$950.20