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	$36.57	10.591%	$40.4431	$40.44	$40.45	$40.40
Purchase #2	$224.94	3.554%	$232.9344	$232.93	$232.95	$232.90
Purchase #3	$48.33	9.789%	$53.061	$53.06	$53.05	$53.10
Purchase #4	$85.76	8.293%	$92.8721	$92.87	$92.85	$92.90
Purchase #5	$182.46	12.634%	$205.512	$205.51	$205.50	$205.50
Purchase #6	$86.65	4.445%	$90.5016	$90.50	$90.50	$90.50
Purchase #7	$203.94	8.740%	$221.7644	$221.76	$221.75	$221.80
7 purchase totals =	$868.65		$937.0886	$937.07	$937.05	$937.10