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	$55.28	7.475%	$59.4122	$59.41	$59.40	$59.40
Purchase #2	$51.48	4.689%	$53.8939	$53.89	$53.90	$53.90
Purchase #3	$36.61	10.260%	$40.3662	$40.37	$40.35	$40.40
Purchase #4	$220.33	10.463%	$243.3831	$243.38	$243.40	$243.40
Purchase #5	$236.45	12.386%	$265.7367	$265.74	$265.75	$265.70
Purchase #6	$87.49	9.330%	$95.6528	$95.65	$95.65	$95.70
Purchase #7	$163.28	3.797%	$169.4797	$169.48	$169.50	$169.50
7 purchase totals =	$850.92		$927.9246	$927.92	$927.95	$928.00