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	$73.99	9.286%	$80.8607	$80.86	$80.85	$80.90
Purchase #2	$78.25	9.300%	$85.5273	$85.53	$85.55	$85.50
Purchase #3	$196.57	3.430%	$203.3124	$203.31	$203.30	$203.30
Purchase #4	$99.60	3.734%	$103.3191	$103.32	$103.30	$103.30
Purchase #5	$85.96	3.422%	$88.9016	$88.90	$88.90	$88.90
Purchase #6	$44.94	8.822%	$48.9046	$48.90	$48.90	$48.90
Purchase #7	$185.43	5.573%	$195.764	$195.76	$195.75	$195.80
7 purchase totals =	$764.74		$806.5897	$806.58	$806.55	$806.60