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	$68.40	10.378%	$75.4986	$75.50	$75.50	$75.50
Purchase #2	$32.72	12.728%	$36.8846	$36.88	$36.90	$36.90
Purchase #3	$6.68	10.475%	$7.3797	$7.38	$7.40	$7.40
Purchase #4	$120.55	6.581%	$128.4834	$128.48	$128.50	$128.50
Purchase #5	$125.78	11.626%	$140.4032	$140.40	$140.40	$140.40
Purchase #6	$72.56	13.181%	$82.1241	$82.12	$82.10	$82.10
Purchase #7	$169.86	6.292%	$180.5476	$180.55	$180.55	$180.50
7 purchase totals =	$596.55		$651.3212	$651.31	$651.35	$651.30