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	$133.87	4.782%	$140.2717	$140.27	$140.25	$140.30
Purchase #2	$31.49	7.658%	$33.9015	$33.90	$33.90	$33.90
Purchase #3	$82.46	3.458%	$85.3115	$85.31	$85.30	$85.30
Purchase #4	$73.59	10.558%	$81.3596	$81.36	$81.35	$81.40
Purchase #5	$124.67	9.530%	$136.5511	$136.55	$136.55	$136.60
Purchase #6	$234.41	13.443%	$265.9217	$265.92	$265.90	$265.90
Purchase #7	$46.90	7.672%	$50.4982	$50.50	$50.50	$50.50
7 purchase totals =	$727.39		$793.8153	$793.81	$793.75	$793.90